Modified layered transition metal oxide material as well as preparation method and application thereof

Abstract

The invention relates to the technical field of sodium ion batteries, in particular to a modified layered transition metal oxide material and a preparation method and application thereof. The modified layered transition metal oxide material comprises a doped and modified layered transition metal oxide core and a coating layer coating the surface of the core, the core of the doped and modified layered transition metal oxide is Na < x > Ni Mn M < c > O < 2 >, xlt; 1, 0lt; a < lt >; 0.33, 0 lt; blt; 0.67, a + b + c = 1; m is selected from at least three of Ti < 4 + >, Zn < 2 + >, Mg < 2 + >, Cu < 2 + >, W < 5 + >, Mo < 4 + >, Sn < 4 + >, Sb < 5 + >, Zr < 4 + >, Al < 3 + >, Fe < 3 + >, Ca < 2 + >, V < 3 + >, Y < 3 + > or Ce < 4 + > ions; and the coating layer comprises the following components: carbon and sodium titanium phosphate. The modified layered transition metal oxide material provided by the invention has excellent stability and cycle performance.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery technology, and in particular to a modified layered transition metal oxide material, its preparation method, and its application. Background Technology

[0002] Compared to lithium-ion batteries, sodium-ion batteries have higher rate capability, wider temperature adaptability, lower cost, and better safety, making them one of the key areas of future new energy research.

[0003] Cathode materials, as one of the key materials in batteries, affect the electrochemical performance of the battery. Currently, cathode materials for sodium-ion batteries mainly include layered transition metal oxides, Prussian blue-based materials, and polyanionic cathode materials. Among these, layered transition metal oxides have become a research hotspot due to their advantages such as high specific energy, abundant resources, environmental friendliness, and simple processing. However, layered transition metal oxides suffer from phase transitions under high pressure, lattice distortion caused by the Jahn-Teller effect, and Mn... 3+ The disproportionation of the substance causes problems such as dissolution of transition metal elements and poor air stability, resulting in poor cycle life of batteries using it and restricting its industrial application.

[0004] Therefore, it is desirable to provide a modified layered transition metal oxide to solve the above problems. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a modified layered transition metal oxide material, its preparation method, and its applications. The modified layered transition metal oxide material provided by this invention suppresses the Jahn-Teller effect of Mn element through high-entropy element doping, improves structural stability, and alleviates high-voltage phase transitions. Simultaneously, coating the surface of the layered transition metal oxide with sodium titanium phosphate / carbon with a Nasicon structure further reduces the dissolution of transition metal elements, thereby effectively improving the stability of the modified layered transition metal oxide material and the cycle life of the battery.

[0006] In a first aspect, the present invention provides a modified layered transition metal oxide material, the modified layered transition metal oxide material comprising a doped modified layered transition metal oxide core and a coating layer covering the surface of the core; The doped and modified layered transition metal oxide core is Na. x Ni a Mn b M c O2, Among them, 0.5 <x<1,0<a<0.33,0<b<0.67,a+b+c=1; M is selected from Ti 4+ Zn2+ Mg 2+ Cu 2+ W 5+ Mo 4+ Sn 4+ Sb 5+ Zr 4+ Al 3+ Fe 3+ Ca 2+ V 3+ Y 3+ or Ce 4+ At least three of the ions; The coating layer is composed of carbon and sodium titanium phosphate.

[0007] The modified layered transition metal oxide material provided by this invention utilizes the synergistic effect of medium- and high-entropy element doping and an outer sodium titanate / carbon coating layer to effectively improve the problems of poor structural stability and poor cycle life of P2-type layered oxide cathode materials. Specifically, this invention introduces the medium- and high-entropy element M to suppress the Jahn-Teller effect of Mn, improve structural stability, and alleviate high-voltage phase transition. At the same time, the sodium titanate in the coating layer has a Nasicon structure, which has a three-dimensional framework structure containing sodium ion transport channels, exhibiting high ionic conductivity and excellent chemical and thermal stability. This effectively avoids side reactions between the layered transition metal oxide core and the electrolyte, thereby enabling the modified layered transition metal oxide material provided by this invention to have excellent stability and cycle performance.

[0008] This invention effectively suppresses the Jahn-Teller effect of Mn element, improves structural stability, and alleviates high-voltage phase transition by doping with at least three medium- to high-entropy elements, thereby effectively improving the stability and cycle performance of cathode materials.

[0009] As a preferred embodiment of the present invention, the D50 particle size of the doped and modified layered transition metal oxide core is 2-5 μm, such as 2 μm, 3 μm, 4 μm, 5 μm, etc.

[0010] As a preferred embodiment of the present invention, with c being 100%, the molar content of any one of the at least three ions selected by M is 7-80%, such as 7%, 10%, 20%, 40%, 60%, 80%, etc., preferably 20-60%.

[0011] As a preferred embodiment of the present invention, based on the total mass of the modified layered transition metal oxide material as 100%, the content of the coating layer is 5-30%, such as 5%, 10%, 15%, 20%, 25%, 30%, etc. If the content of the coating layer is too low, the improvement effect is limited; if the content of the coating layer is too high, it will lead to a decrease in the capacity utilization and energy density of the cathode material after coating.

[0012] As a preferred embodiment of the present invention, the carbon content is 0.5-3% based on the total mass of the coating layer as 100%, for example, 0.5%, 1%, 2%, 3%, etc.

[0013] In a second aspect, the present invention provides a method for preparing the modified layered transition metal oxide material as described in the first aspect, the method comprising: (1) Disperse Na source, Ni source, Mn source and M source in solvent, mix well, spray dry, and then sinter to obtain doped modified layered transition metal oxide core. (2) Disperse the Na source, Ti source, P source and carbon source in a solvent and mix them to obtain sodium titanium phosphate precursor slurry; (3) The doped and modified layered transition metal oxide core and the sodium titanium phosphate precursor slurry are mixed, spray-dried and calcined to obtain the modified layered transition metal oxide material.

[0014] The preparation method provided by this invention is simple. By using wet coating, the coating layer is completely and uniformly coated on the surface of the layered transition metal oxide core, and the modified layered transition metal oxide material obtained is more stable in structure.

[0015] As a preferred embodiment of the present invention, the Na source is selected from any one or more of sodium carbonate, sodium bicarbonate, and sodium hydroxide.

[0016] As a preferred embodiment of the present invention, the Ni source is selected from any one or more of nickel monoxide, nickel trioxide, nickel tetroxide, nickel hydroxide, nickel sulfate, and nickel acetate.

[0017] As a preferred embodiment of the present invention, the Mn source is selected from any one or more of manganese carbonate, manganese dioxide, manganese tetroxide, manganese acetate, and manganese trioxide.

[0018] As a preferred embodiment of the present invention, the M source is selected from any one or more of the oxides, hydroxides, carbonates, oxalates, chlorides, nitrates, and sulfates corresponding to the M element.

[0019] As a preferred embodiment of the present invention, the Ti source is selected from titanium dioxide and / or titanium phosphate.

[0020] As a preferred embodiment of the present invention, the P source is selected from any one or more of phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, sodium phosphate, and ammonium phosphate.

[0021] As a preferred embodiment of the present invention, the molar ratio of Na element in the Na source, Ti element in the Ti source, and P element in the P source is 1:2:3.

[0022] As a preferred embodiment of the present invention, the carbon source is selected from any one or more of glucose, sucrose, carbon nanotubes and graphite.

[0023] As a preferred technical solution of the present invention, the mixing method in step (1) is sand milling, and the particle size of the slurry after sand milling is less than 300 nm.

[0024] As a preferred technical solution of the present invention, the solid content of the slurry after mixing in step (1) is 30-60%, for example 30%, 40%, 50%, 60%, etc.

[0025] As a preferred technical solution of the present invention, the spray drying temperature in step (1) is 130-200℃, for example 130℃, 150℃, 180℃, 200℃, etc.

[0026] As a preferred technical solution of the present invention, the sintering in step (1) is carried out in an air or oxygen atmosphere.

[0027] As a preferred technical solution of the present invention, the sintering temperature in step (1) is 850-1000℃ (e.g., 850℃, 900℃, 950℃, 1000℃, etc.), and the sintering time is 8-24h (e.g., 8h, 12h, 16h, 20h, 24h, etc.).

[0028] As a preferred technical solution of the present invention, after sintering in step (1), the material is further pulverized so that the D50 particle size of the obtained doped modified layered transition metal oxide core is within the target range.

[0029] As a preferred technical solution of the present invention, the mixing method in step (2) is sand milling.

[0030] As a preferred embodiment of the present invention, the D50 particle size of the sodium titanium phosphate precursor slurry is 0.1-0.2 μm, such as 0.1 μm, 0.12 μm, 0.14 μm, 0.16 μm, 0.18 μm, 0.2 μm, etc.

[0031] As a preferred embodiment of the present invention, the solid content of the sodium titanium phosphate precursor slurry is 30-60%, for example, 30%, 40%, 50%, 60%, etc.

[0032] As a preferred technical solution of the present invention, the spray drying temperature in step (3) is 150-200℃, such as 150℃, 160℃, 170℃, 180℃, 190℃, 200℃, etc.

[0033] As a preferred technical solution of the present invention, the spray drying and calcination in step (3) are carried out in an inert gas atmosphere, wherein the inert gas is selected from any one of nitrogen, argon and helium.

[0034] As a preferred technical solution of the present invention, the calcination temperature in step (3) is 600-800℃ (e.g., 600℃, 650℃, 700℃, 750℃, 800℃, etc.), and the calcination time is 8-24h (e.g., 8h, 12h, 16h, 20h, 24h, etc.).

[0035] As a preferred technical solution of the present invention, the step (3) of mixing the doped modified layered transition metal oxide core and the sodium titanium phosphate precursor slurry includes: mixing the doped modified layered transition metal oxide core with a dispersant and a solvent to obtain a pre-dispersed slurry, and then mixing the pre-dispersed slurry with the sodium titanium phosphate precursor slurry.

[0036] As a preferred embodiment of the present invention, the dispersant is selected from polyethylene glycol and / or polyvinylpyrrolidone.

[0037] As a preferred embodiment of the present invention, the mass ratio of the dispersant to the doped and modified layered transition metal oxide core is 0.5-1:100, for example, 0.5:100, 0.6:100, 0.7:100, 0.8:100, 0.9:100, 1:100, etc.

[0038] As a preferred embodiment of the present invention, the solid content of the pre-dispersed slurry is 30-60%, for example, 30%, 40%, 50%, 60%, etc.

[0039] Thirdly, the present invention provides a positive electrode sheet, the positive electrode sheet comprising the modified layered transition metal oxide material described in the first aspect or the modified layered transition metal oxide material prepared by the preparation method described in the second aspect.

[0040] Fourthly, the present invention provides a sodium-ion battery, the sodium-ion battery comprising the positive electrode sheet described in the third aspect.

[0041] The technical solution provided by the embodiments of the present invention has the following advantages compared with the prior art: The modified layered transition metal oxide material provided by this invention suppresses the Jahn-Teller effect of Mn element through medium- and high-entropy element doping, improves structural stability, and alleviates high-voltage phase transition. At the same time, the Nasicon structure of sodium titanium phosphate / C is coated on the surface of the layered transition metal oxide to further reduce the dissolution of transition metal elements, thereby effectively improving the stability of the modified layered transition metal oxide material and the cycle life of the battery. Detailed Implementation

[0042] To better understand the above-mentioned objectives, features, and advantages of the present invention, the solutions of the present invention will be further described below. It should be noted that, unless otherwise specified, the embodiments of the present invention and the features thereof can be combined with each other.

[0043] Many specific details are set forth in the following description in order to provide a full understanding of the invention, but the invention may also be practiced in other ways different from those described herein; obviously, the embodiments in the specification are only some embodiments of the invention, and not all embodiments.

[0044] Example 1 This embodiment provides a modified layered transition metal oxide material and its preparation method. The modified layered transition metal oxide material includes a doped and modified layered transition metal oxide core Na. 0.67 Ni 0.27 Mn 0.57 Ti 0.1 Zn 0.0 3Mg 0.03 O2 and a coating layer covering the surface of the core, wherein the coating layer comprises carbon and sodium titanium phosphate, and the coating layer content is 10% based on 100% of the total mass of the modified layered transition metal oxide material, and the carbon content is 2% based on 100% of the total mass of the coating layer; The preparation method includes the following steps: (1) According to the Na:Ni:Mn:Ti:Zn:Mg molar ratio of 0.67:0.27:0.57:0.1:0.03:0.03, the corresponding Na2CO3, NiO, MnCO3, TiO2, ZnO and MgO were dispersed in deionized water with a solid content of 40%. The mixture was sand-milled to obtain a slurry with a D50 particle size of less than 300 nm. It was spray-dried at 180 °C and then sintered at 900 °C for 18 h in air atmosphere. The sintered material was pulverized to D50 < 5 μm to obtain a doped modified layered transition metal oxide core. (2) The doped and modified layered transition metal oxide core is mixed with polyethylene glycol and water, wherein the mass of polyethylene glycol is 5% of the mass of the doped and modified layered transition metal oxide core, to obtain a pre-dispersed slurry with a solid content of 50%. (3) Prepare a slurry with the mass of carbon-sodium titanium phosphate accounting for 10% of the mass of the final product material. Disperse the corresponding Na2CO3, TiO2, H3PO4 and glucose in water, wherein the glucose is prepared with a carbon content of 2% and the slurry solid content is 30%. Grind this mixed slurry to obtain sodium titanium phosphate precursor slurry with D50<0.2μm. (4) The pre-dispersed slurry from step (2) is added to the sodium titanium phosphate precursor slurry from step (3) and mixed. The mixture is then spray-dried at 180°C in a nitrogen atmosphere and sintered at 700°C for 12 h in a nitrogen atmosphere to obtain the modified layered transition metal oxide material.

[0045] Example 2 This embodiment provides a modified layered transition metal oxide material and its preparation method. The modified layered transition metal oxide material includes a doped and modified layered transition metal oxide core Na. 0.66 Ni 0.30 Mn 0.57 Ti 0.05 Mo 0.0 5Cu 0.02 Al 0.01 O2 and a coating layer covering the surface of the core, wherein the coating layer comprises carbon and sodium titanium phosphate, and the coating layer content is 10% based on 100% of the total mass of the modified layered transition metal oxide material, and the carbon content is 2% based on 100% of the total mass of the coating layer; The preparation method is described in Example 1, where the doping elements correspond to the raw materials TiO2, MoO2, CuO, and Al2O3, respectively.

[0046] Example 3 This embodiment provides a modified layered transition metal oxide material and its preparation method, wherein the modified layered transition metal oxide material is the same as that in Example 1; The preparation method is described in reference to Example 1. The difference between Example 1 and Example 1 is that in this example, in step (1), the raw materials Na2CO3, NiO, and MnCO3 are replaced with NaHCO3, NiSO4, and MnO2, respectively; in step (3), the raw materials Na2CO3, TiO2, H3PO4, and glucose are replaced with NaOH, titanium phosphate, (NH4)2HPO4, and sucrose, respectively.

[0047] Example 4 This embodiment provides a modified layered transition metal oxide material and its preparation method. The modified layered transition metal oxide material includes a doped and modified layered transition metal oxide core Na. 0.67 Ni 0.27 Mn 0.57 Ti 0.1 Zn 0.0 3Mg 0.03 O2 and a coating layer covering the surface of the core, wherein the coating layer comprises carbon and sodium titanium phosphate, and the coating layer content is 30% based on 100% of the total mass of the modified layered transition metal oxide material, and the carbon content is 2% based on 100% of the total mass of the coating layer; The preparation method is described in Example 1.

[0048] Example 5 This embodiment provides a modified layered transition metal oxide material and its preparation method. The modified layered transition metal oxide material includes a doped and modified layered transition metal oxide core Na. 0.67 Ni 0.27 Mn 0.57 Ti 0.1 Zn 0.0 3Mg 0.03 O2 and a coating layer covering the surface of the core, the coating layer comprising carbon and sodium titanium phosphate, wherein the coating layer content is 5% based on 100% of the total mass of the modified layered transition metal oxide material, and the carbon content is 0.5% based on 100% of the total mass of the coating layer; The preparation method includes the following steps: (1) According to the molar ratio of Na:Ni:Mn:Ti:Zn:Mg of 0.67:0.27:0.57:0.1:0.03:0.03, the corresponding Na2CO3, NiO, MnCO3, TiO2, ZnO and MgO were dispersed in deionized water with a solid content of 40%. The mixture was sand-milled to obtain a slurry with a D50 particle size of less than 300 nm. It was spray-dried at 150 °C and then sintered at 1000 °C for 10 h in air atmosphere. The sintered material was pulverized to D50 < 5 μm to obtain a doped modified layered transition metal oxide core. (2) The doped and modified layered transition metal oxide core is mixed with polyethylene glycol and water, wherein the mass of polyethylene glycol is 5% of the mass of the doped and modified layered transition metal oxide core, to obtain a pre-dispersed slurry with a solid content of 50%. (3) Prepare a slurry with the mass of carbon-sodium titanium phosphate accounting for 5% of the mass of the final product material. Disperse the corresponding Na2CO3, TiO2, H3PO4 and glucose in water, wherein the glucose is prepared with a carbon content of 0.5% and the solid content of the slurry is 30%. Grind this mixed slurry to obtain a sodium titanium phosphate precursor slurry with D50<0.2μm. (4) The pre-dispersed slurry from step (2) is added to the sodium titanium phosphate precursor slurry from step (3) and mixed. The mixture is then spray-dried at 200°C in a nitrogen atmosphere and sintered at 800°C for 8 h in a nitrogen atmosphere to obtain the modified layered transition metal oxide material.

[0049] Comparative Example 1 This comparative example provides a modified layered transition metal oxide material and its preparation method. The modified layered transition metal oxide material is the doped modified layered transition metal oxide core prepared in step (1) of Example 1, without an external coating layer. The preparation method is the same as step (1) in Example 1.

[0050] Comparative Example 2 This comparative example provides a modified layered transition metal oxide material and its preparation method. The modified layered transition metal oxide material is the same as that in Example 1, except that the core in this comparative example is Na. 0.67 Ni 0.33 Mn 0.67 O2, meaning no elemental doping; The preparation method is the same as in Example 1.

[0051] Comparative Example 3 This comparative example provides a modified layered transition metal oxide material and its preparation method. The modified layered transition metal oxide material is the same as that in Example 1, except that the core in this comparative example is Na. 0.67 Ni 0.27 Mn 0.57 Ti 0.1 Zn 0.06 O2; The preparation method is the same as in Example 1.

[0052] Comparative Example 4 This comparative example provides a modified layered transition metal oxide material and its preparation method. The modified layered transition metal oxide material is the same as that in Example 1, except that the core in this comparative example is Na. 0.67 Ni 0.27 Mn 0.57 Ti 0.1 Mg 0.06 O2; The preparation method is the same as in Example 1.

[0053] Comparative Example 5 This comparative example provides a modified layered transition metal oxide material and its preparation method. The modified layered transition metal oxide material is the same as that in Example 1, except that the core in this comparative example is Na. 0.67 Ni 0.27 Mn 0.67 Zn 0.03 Mg 0.03 O2; The preparation method is the same as in Example 1.

[0054] Performance testing 1. The modified layered transition metal oxide materials prepared according to the examples and comparative examples were used to prepare positive electrode sheets and assemble batteries.

[0055] The modified layered transition metal oxide material prepared in the examples and comparative examples was used as the positive electrode active material. It was mixed with SuperP conductive carbon and polyvinylidene fluoride (PVDF) in a mass ratio of 8:1:1 and added to NMP solvent to obtain a positive electrode slurry. The slurry was coated on aluminum foil with a coating thickness of 200 μm and dried to obtain a positive electrode sheet. A coin cell was assembled in a glove box under a high-purity argon atmosphere, with a sodium metal sheet as the counter electrode; the electrolyte was 1 M NaClO4 as the sodium salt; the solvent was a mixture of ethylene carbonate (EC) and propylene carbonate (PC) in a volume ratio of 1:1 with 5 Vol% fluoroethylene carbonate (FEC) added; and glass fiber was used as the separator.

[0056] 2. Perform electrochemical tests within a voltage window range of 2.5~4.3V.

[0057] The specific testing method is to first perform three activation cycles at a 0.1 C rate, followed by a 1 C long-cycle test.

[0058] The test results are shown in Table 1: Table 1

[0059] Table 1 shows that the modified layered transition metal oxide material provided by this invention exhibits superior cycling performance compared to the comparative examples. It is noteworthy that, compared to Example 1 without coating modification, Comparative Example 1, while showing higher capacity utilization without an inert coating, exhibits significantly poorer cycling stability. Comparative Example 2, without active core doping modification, has a higher proportion of active nickel, thus demonstrating higher initial capacity utilization. However, its structural instability, Mn dissolution problem, and severe high-pressure material phase transition problem remain unresolved, resulting in very poor material stability. Even with external coating modification, it is difficult to effectively prevent performance degradation during cycling. These differences further highlight the effectiveness of the composite modification brought about by internal high-entropy element doping and external sodium titanium phosphate / carbon coating in this invention.

[0060] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0061] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention is not to be limited to the embodiments described herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A modified layered transition metal oxide material, characterized in that, The modified layered transition metal oxide material includes a doped and modified layered transition metal oxide core and a coating layer covering the surface of the core; The doped and modified layered transition metal oxide core is Na. x Ni a Mn b M c O2, Among them, 0.5 <x<1,0<a<0.33,0<b<0.67,a+b+c=1; M is selected from Ti 4+ Zn 2+ Mg 2+ Cu 2+ W 5+ Mo 4+ Sn 4+ Sb 5+ Zr 4+ Al 3+ Fe 3+ Ca 2+ V 3+ Y 3+ or Ce 4+ At least three of the ions; The coating layer is composed of carbon and sodium titanium phosphate.

2. The modified layered transition metal oxide material according to claim 1, characterized in that, The D50 particle size of the doped and modified layered transition metal oxide core is 2-5 μm; And / or, with c being 100%, the molar content of any one of the at least three ions selected by M is 7-80%.

3. The modified layered transition metal oxide material according to claim 1 or 2, characterized in that, Based on the total mass of the modified layered transition metal oxide material being 100%, the content of the coating layer is 5-30%; And / or, based on the total mass of the coating layer being 100%, the carbon content is 0.5-3%.

4. The method for preparing the modified layered transition metal oxide material according to any one of claims 1-3, characterized in that, The preparation method includes: (1) Disperse Na source, Ni source, Mn source and M source in solvent, mix well, spray dry, and then sinter to obtain doped modified layered transition metal oxide core. (2) Disperse the Na source, Ti source, P source and carbon source in a solvent and mix them to obtain sodium titanium phosphate precursor slurry; (3) The doped and modified layered transition metal oxide core and the sodium titanium phosphate precursor slurry are mixed, spray-dried and calcined to obtain the modified layered transition metal oxide material.

5. The preparation method according to claim 4, characterized in that, The Na source is selected from any one or more of sodium carbonate, sodium bicarbonate, and sodium hydroxide. And / or, the Ni source is selected from any one or more of nickel monoxide, nickel trioxide, nickel tetroxide, nickel hydroxide, nickel sulfate, and nickel acetate; And / or, the Mn source is selected from any one or more of manganese carbonate, manganese dioxide, manganese tetroxide, manganese acetate, and manganese trioxide; And / or, the M source is selected from any one or more of the oxides, hydroxides, carbonates, oxalates, chlorides, nitrates and sulfates corresponding to the M element; And / or, the Ti source is selected from titanium dioxide and / or titanium phosphate; And / or, the P source is selected from any one or more of phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, sodium phosphate, and ammonium phosphate; And / or, the carbon source is selected from any one or more of glucose, sucrose, carbon nanotubes and graphite.

6. The preparation method according to claim 4 or 5, characterized in that, The mixing method described in step (1) is sand milling, and the particle size of the slurry after sand milling is less than 300 nm; And / or, the spray drying temperature in step (1) is 130-200°C; And / or, the sintering described in step (1) is carried out in an air or oxygen atmosphere; And / or, the sintering temperature in step (1) is 850-1000℃ and the sintering time is 8-24h; And / or, after sintering as described in step (1), the material is further pulverized.

7. The preparation method according to any one of claims 4-6, characterized in that, The mixing method described in step (2) is sand milling; And / or, the D50 particle size of the sodium titanium phosphate precursor slurry is 0.1-0.2 μm; And / or, the spray drying temperature in step (3) is 150-200°C; And / or, the spray drying and calcination in step (3) are both carried out under an inert gas atmosphere; And / or, the calcination temperature in step (3) is 600-800℃ and the calcination time is 8-24h.

8. The preparation method according to any one of claims 4-7, characterized in that, Step (3) involves mixing the doped and modified layered transition metal oxide core and the sodium titanium phosphate precursor slurry. This includes mixing the doped and modified layered transition metal oxide core with a dispersant and a solvent to obtain a pre-dispersed slurry, and then mixing the pre-dispersed slurry with the sodium titanium phosphate precursor slurry. Preferably, the dispersant is selected from polyethylene glycol and / or polyvinylpyrrolidone.

9. A positive electrode sheet, characterized in that, The positive electrode sheet comprises the modified layered transition metal oxide material according to any one of claims 1-3 or the modified layered transition metal oxide material prepared by the preparation method according to any one of claims 4-8.

10. A sodium-ion battery, characterized in that, The sodium-ion battery includes the positive electrode sheet as described in claim 9.

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