Modification method of sodium electrode layered transition metal oxide positive electrode material

Abstract

The invention relates to a modification method of a sodium electrode layered transition metal oxide positive electrode material, which comprises the following steps: dissolving a layered oxide positive electrode material NFM with an O3 type structure in a modification solvent, heating and stirring, carrying out suction filtration, drying, and carrying out heat treatment to obtain modified positive electrode material powder. Compared with the prior art, simple reagent treatment is utilized, residual alkali components on the surface of the sodium battery positive electrode material are greatly reduced, and negative effects caused by the residual alkali components are reduced. And meanwhile, the surface of the material can be coated or a stable positive electrode material / electrolyte interface film CEI can be formed in the circulation process, so that the positive electrode material interface is stabilized, and the problem of failure of the positive electrode of the sodium ion battery is relieved. When the composite material is used for the sodium-ion battery, the rate capability and the long cycle performance of the sodium-ion battery are improved, and the service life of the sodium-ion battery is prolonged.

Description

Technical Field

[0001] The present invention belongs to the technical field of rechargeable sodium secondary batteries, and relates to a modification method for a layered transition metal oxide cathode material for sodium batteries. Background Art

[0002] In recent years, the uneven geopolitical distribution and drastic price fluctuations of lithium resources have accelerated the strategic layout of new energy storage systems. Among them, sodium-ion batteries have become the most promising secondary battery supplementary system with industrialization potential due to their significant advantages in resource reserves (crustal abundance of 2.74% vs. 0.0065% for lithium), high equipment compatibility with the lithium battery industry, and better environmental adaptability.

[0003] However, during the preparation of sodium layered oxide cathode materials, residual alkali components such as NaOH / NaHCO 3 / Na 2 CO 3 will inevitably be generated. These residual alkalis lead to the problem of slurry gelation during the processing, significantly increasing the coating difficulty of the electrode slurry. During cycling, the insulating surface residual alkali will significantly increase the interfacial impedance, hindering the diffusion of Na+ at the interface. In addition, due to the high reactivity of the cathode material surface, the surface side reaction between the electrolyte and the cathode surface accelerates the dissolution of transition metal ions and triggers irreversible surface phase transformation (such as the transformation from layered structure to spinel or rock salt phase).

[0004] Current research on the modification strategies of O3-type layered oxide cathodes (such as NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O 2 , NFM) mostly focuses on bulk optimization. For example, the research team of Wang Wenxu from the University of Shanghai for Science and Technology (J. Energy Storage, 2024) improved the lattice stability by Ta 5+ doping, enabling NFM to maintain a capacity of 102 mA h g -1 even at a high rate of 10C; the research group of Zeng Zhiyong from Yangzhou University (Nano Energy, 2024) extended the cycle life to more than 1000 times by using multi-element high-entropy design. However, the applicant found through research that the above bulk optimization strategies are difficult to solve the inherent problems on the material surface - corrosion by residual alkali (Na 2 CO 3 / NaOH) and degradation of the interfacial structure. In addition, traditional bulk doping or high-entropy design often comes at the cost of sacrificing specific capacity and increasing process complexity.

[0005] Therefore, there is an urgent need to develop an efficient, low-energy-consuming and highly operable method to wash away the residual alkali on the surface of the sodium-ion battery layered oxide cathode material, and at the same time construct a stable surface structure, so as to obtain a sodium-ion battery layered transition metal oxide battery with long cycle life and practical value. Summary of the Invention

[0006] The purpose of the present invention is to provide a modification method for a sodium-ion battery layered transition metal oxide cathode material. By means of surface treatment, the processing performance and electrochemical performance of the layered transition metal oxide cathode material NFM for sodium-ion batteries are improved, thereby improving the rate performance and long cycle performance of sodium-ion batteries and extending their service life.

[0007] The purpose of the present invention can be achieved by the following technical solutions:

[0008] On the one hand, the present invention provides a modification method for a sodium-ion battery layered transition metal oxide cathode material. The layered oxide cathode material NFM with O3-type structure is dissolved in a modification solvent, heated and stirred, then filtered and dried, and then heat-treated to obtain a modified cathode material powder.

[0009] Furthermore, the layered oxide cathode material NFM with O3-type structure used in the present invention has the chemical formula NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O 2 (NFM), in which sodium ions occupy the octahedral void positions, and it has an O3-type structure. Inevitably, residual alkali components such as NaOH and Na 2 CO 3 etc. will be generated during the synthesis and storage processes. This is a conventional existing material in the art and not the innovation point of the present invention, so it will not be elaborated here.

[0010] Furthermore, the modification solvent is ethylene glycol or polyethylene glycol, preferably ethylene glycol.

[0011] Furthermore, the addition ratio of the layered oxide cathode material NFM to the modification solvent is 1 g:(4 - 6) mL, preferably 1 g:5 mL.

[0012] Furthermore, the temperature for heating and stirring is 40 - 80 °C, preferably 60 °C, and the time is 6 - 24 h, preferably 12 h.

[0013] Furthermore, the drying process is: drying overnight at 80 - 120 °C, preferably 100 °C.

[0014] Furthermore, the temperature for heat treatment is 400 - 650 °C, preferably 500 °C.

[0015] Further, the heat treatment time is 4 to 8 h, preferably 6 h.

[0016] In a second aspect, the present invention provides a sodium-ion layered transition metal oxide cathode material, which is obtained by treating with the modification method described in any one of the above.

[0017] In a third aspect, the present invention provides an application of a sodium-ion layered transition metal oxide cathode material in constructing a sodium-ion battery with excellent cycle performance and rate performance.

[0018] Further, the sodium-ion battery is composed of a composite cathode, a separator, an organic electrolyte, and an anode.

[0019] The cathode material obtained by the above modification treatment is mixed with a conductive additive, a binder, and a solvent in a certain ratio (the cathode material: binder: conductive additive is configured according to a mass ratio of 8:1:1, and the binder and the solvent are configured into a solution with a mass fraction of 3.226%), and pulping is carried out. The conductive additive is preferably Super P, the binder is preferably PVDF, and the solvent is preferably N-methylpyrrolidone (NMP); the prepared slurry is coated on a current collector, and the coating operation is completed. The current collector is preferably aluminum foil; then the coated electrode sheet is put into an oven for drying; finally, the dried electrode sheet is cut to obtain a composite cathode of the sodium-ion battery.

[0020] Further, the separator is a glass fiber separator, a ceramic separator, a polymer separator, etc. The present invention preferably uses a GF / D type glass fiber separator.

[0021] Further, the organic electrolyte is a carbonate electrolyte, and the solvent is selected from at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC). The solvent in the organic electrolyte is preferably EC:PC = 1:1, and the solute is selected from sodium hexafluorophosphate (NaPF 6 ), sodium perchlorate (NaClO 4 ), sodium bis(trifluoromethylsulfonyl)imide (NaTFSI), or one or more of them. It is preferably NaClO 4 .

[0022] Further, the anode is one of metallic sodium, metal oxide, hard carbon, etc. The present invention preferably uses metallic sodium as the anode.

[0023] Compared with the prior art, the present invention simply treats the sodium-ion battery layered transition metal oxide cathode material NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O 2 with a modification solvent such as ethylene glycol by heat preservation and stirring, so that NaNi 1 / 3 Fe1 / 3 Mn 1 / 3 O 2 The performance of the cathode for sodium-ion batteries is greatly improved. By using the modification method provided by the present invention, the cycle stability, rate performance, etc. of the material are greatly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 SEM image of the NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O 2 material in Comparative Example 1 of the present invention (i.e., the cathode material before modification).

[0025] Figure 2 XRD pattern of the NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O 2 material in Comparative Example 1 of the present invention (i.e., the cathode material before modification).

[0026] Figure 3 Long cycle performance graph of the NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O 2 material in Comparative Example 1 of the present invention (i.e., the cathode material before modification) at a rate of 1C.

[0027] Figure 4 Rate performance graph of the NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O 2 material in Comparative Example 1 of the present invention (i.e., the cathode material before modification).

[0028] Figure 5 SEM image of the modified NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O 2 material in Example 1 of the present invention.

[0029] Figure 6 XRD pattern of the modified NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O 2 material in Example 1 of the present invention.

[0030] Figure 7 Long cycle performance graph of the modified NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O 2 material in Example 1 of the present invention at a rate of 1C.

[0031] Figure 8 For the modified NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O 2 material in Example 1 of the present invention, the rate performance diagram. Detailed implementation manners

[0032] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. This embodiment is implemented on the premise of the technical solution of the present invention, and the detailed implementation manners and specific operation processes are given, but the protection scope of the present invention is not limited to the following embodiments.

[0033] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which this application belongs. The terms used in the description of this application herein are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0034] As used herein, the alternative ranges of the terms "and / or", "or / and", "and / or" include any one of two or more related listed items, and also include any and all combinations of the related listed items. The said any and all combinations include combinations of any two related listed items, any more related listed items, or all related listed items. It should be noted that when at least two conjunctions selected from "and / or", "or / and", "and / or" are used to connect at least three items, it should be understood that in this application, this technical solution undoubtedly includes the technical solution connected by "logical AND", and undoubtedly also includes the technical solution connected by "logical OR".

[0035] In this application, among the technical features described in an open-ended manner, it includes a closed technical solution composed of the listed features, and also includes an open technical solution containing the listed features.

[0036] In this application, regarding the numerical range, unless otherwise specified, the above numerical range is considered continuous and includes the minimum value and the maximum value of this range, as well as each value between such minimum value and maximum value. Further, when the range refers to an integer, it includes each integer between the minimum value and the maximum value of this range. In addition, when multiple ranges are provided to describe features or characteristics, these ranges can be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all sub-ranges subsumed therein.

[0037] This document specifically discloses only some numerical ranges. However, any lower limit can be combined with any upper limit to form a range not explicitly recited; and any lower limit can be combined with other lower limits to form a range not explicitly recited, and similarly any upper limit can be combined with any other upper limit to form a range not explicitly recited. In addition, each individually disclosed point or single numerical value itself can be used as a lower limit or an upper limit and combined with any other point or single numerical value or combined with other lower limits or upper limits to form a range not explicitly recited.

[0038] For the temperature parameters in this application, unless otherwise specified, both constant temperature treatment and treatment within a certain temperature range are allowed. The constant temperature treatment allows the temperature to fluctuate within the accuracy range controlled by the instrument. Fluctuation within ranges such as ±5°C, ±4°C, ±3°C, ±2°C, ±1°C is allowed.

[0039] In this document, the "suitable" in expressions such as "suitable combination method", "suitable method", "any suitable method", etc. is subject to being able to implement the technical solution of this application, solve the technical problems of this application, and achieve the expected technical effects of this application.

[0040] In this application, terms such as "further", "even further", "especially", etc. are used for descriptive purposes and indicate differences in content, but should not be construed as limiting the scope of protection of this application.

[0041] In this application, "optionally", "optional", "option", mean having or not having, that is, any one selected from two alternative schemes of "having" or "not having". If "optional" appears multiple times in a technical solution, unless otherwise specified and there are no contradictions or mutual restrictions, each "optional" is independent.

[0042] In the description of the application, the meaning of "a variety of" is at least two, such as two, three, etc., unless otherwise specifically defined.

[0043] Unless otherwise specified, all preparations and tests in this document are carried out in an environment of 25°C.

[0044] In this document, "comprises", "includes", "contains", "has", or other variants are intended to cover non-closed inclusion, and no distinction is made between these terms. The term "contains" means that other steps and components can be added without affecting the final result. The compositions and methods / processes of the present invention comprise, consist of, and consist essentially of the essential elements and limitations described herein and any additional or optional components, ingredients, steps, or limitations described herein. In this document, no distinction is made between the terms "efficacy", "performance", "effect", and "function".

[0045] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution. Unless otherwise specified, all technical features and optional technical features of the present application can be combined with each other to form a new technical solution.

[0046] Unless otherwise specified, all steps of the present application can be carried out sequentially or randomly, preferably sequentially.

[0047] In the following examples, the sodium-ion batteries used are composed of a composite cathode, a separator, an organic electrolyte, and an anode. Among them, the preparation process of the composite cathode is as follows: the modified cathode material is mixed with a conductive additive, a binder (PVDF), and a solvent (N-methylpyrrolidone, NMP), and pulping is carried out. The mass ratio of the cathode material: binder: conductive additive is 8:1:1, and the binder and the solvent are configured into a solution with a mass fraction of 3.226%.

[0048] The separator used is a GF / D type glass fiber separator;

[0049] The solvent in the organic electrolyte is EC:PC = 1:1, and the solute is NaClO 4 , and the molar fraction of the solute in the organic electrolyte is 10 mol / L;

[0050] The anode uses metallic sodium.

[0051] For the remaining raw materials or processing techniques without special instructions, it means that they are all conventional commercially available raw materials or conventional processing techniques in the art.

[0052] Example 1:

[0053] (1) Preparation of the original cathode material: According to the stoichiometric ratios of the elements in NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O 2 , accurately weigh Na 2 CO 3 , NiO, Fe 2 O 3 , MnO 2 , ball mill for 10 h, keep the pressure at 20 Mpa for 1 min, press the powder into a disc with a diameter of 14 mm, and calcine at 950 °C to obtain the pre-modified cathode material. Attached Figure 1 is the SEM image of the pre-modified cathode material, which is characterized by a blocky shape, fine surface, and a large amount of residual alkali components. Attached Figure 2 is the XRD pattern of the pre-modified cathode material, and its structure shows an O3 structure.

[0054] (2) Dissolve the as-prepared pristine cathode material in ethylene glycol at a ratio of 1 g NFM: 5 mL ethylene glycol, and then stir the solution at 60 °C for 12 h. After suction filtration of the treated solution, it is found that the obtained filtrate is purplish red, indicating that in addition to the dissolution of residual alkali during heating and stirring, there is also a surface reaction. Dry the powder obtained by suction filtration overnight in a vacuum oven at 100 °C. Subsequently, heat-treat the dried powder at 500 °C for 6 h to further reduce the residual alkali on the surface of the original NFM and construct a stable interface, thereby obtaining the modified cathode material powder.

[0055] Attachment Figure 5 is the SEM image of the modified cathode material. After treatment, the bulk structure of the material is maintained, and a large amount of residual alkali on the surface is removed, and the surface is smooth. Attachment Figure 2 is the XRD pattern of the modified cathode material, indicating that the O3 structure of the treated material is not destroyed. At the same time, the 003 peak shifts to the left. According to the Bragg diffraction equation, the c-axis spacing of the treated material increases, widening the sodium ion deintercalation channel, thereby improving the rate performance.

[0056] (3) Prepare a composite cathode using the above-mentioned modified cathode material.

[0057] (4) Assemble a CR2032 coin cell in the order of the negative electrode case, negative electrode, separator, electrolyte, gasket, spring piece, and positive electrode case.

[0058] (5) Test the assembled sodium-ion battery using a Neware constant temperature charge-discharge tester. After activation at a rate of 0.1C, perform long-cycle constant current charge-discharge tests and rate tests at a rate of 1C.

[0059] Comparative Example 1

[0060] (1) Prepare the pristine cathode material (the specific steps are the same as in Example 1).

[0061] (2) Without any treatment, prepare a composite cathode using the above-mentioned cathode material.

[0062] (3) Assembly of the sodium-ion battery (the specific steps are the same as in Example 1).

[0063] (4) Performance test of the sodium-ion battery (the specific steps are the same as in Example 1).

[0064] Comparative Example 2

[0065] (1) Prepare the pristine cathode material (the specific steps are the same as in Example 1).

[0066] (2) Without subsequent heat treatment, the remaining steps are the same as in Example 1.

[0067] (3) Prepare a composite cathode using the above-mentioned cathode material.

[0068] (IV) Sodium-ion battery assembly (the specific steps are the same as those in Example 1).

[0069] (V) Sodium-ion battery performance test (the specific steps are the same as those in Example 1).

[0070] Comparative Example 3

[0071] (I) Prepare the original cathode material (the specific steps are the same as those in Example 1).

[0072] (II) Treat it with ethanol as the modification reagent, and the remaining steps are the same as those in Example 1.

[0073] (III) Prepare a composite cathode using the above cathode material.

[0074] (IV) Sodium-ion battery assembly (the specific steps are the same as those in Example 1).

[0075] (V) Sodium-ion battery performance test (the specific steps are the same as those in Example 1).

[0076] Comparative Example 4

[0077] (I) Prepare the original cathode material (the specific steps are the same as those in Example 1).

[0078] (II) Treat it with dimethylformamide (DMF) as the modification reagent, and the remaining steps are the same as those in Example 1. (III) Prepare a composite cathode using the above cathode material.

[0079] (IV) Sodium-ion battery assembly (the specific steps are the same as those in Example 1).

[0080] (V) Sodium-ion battery performance test (the specific steps are the same as those in Example 1).

[0081] Example 2

[0082] (I) Prepare the original cathode material (the specific steps are the same as those in Example 1).

[0083] (II) Treat it with polyethylene glycol as the modification reagent, and the remaining steps are the same as those in Example 1.

[0084] (III) Prepare a composite cathode using the above cathode material.

[0085] (IV) Sodium-ion battery assembly (the specific steps are the same as those in Example 1).

[0086] (V) Sodium-ion battery performance test (the specific steps are the same as those in Example 1).

[0087] Example 3

[0088] (I) Prepare the original cathode material (the specific steps are the same as those in Example 1).

[0089] (2) Set the stirring temperature to 20 °C, and the remaining steps are the same as in Example 1.

[0090] (3) Prepare a composite positive electrode using the above positive electrode material.

[0091] (4) Assemble a sodium-ion battery (the specific steps are the same as in Example 1).

[0092] (5) Test the performance of the sodium-ion battery (the specific steps are the same as in Example 1).

[0093] Example 4

[0094] (1) Prepare the original positive electrode material (the specific steps are the same as in Example 1).

[0095] (2) Set the stirring temperature to 40 °C, and the remaining steps are the same as in Example 1.

[0096] (3) Prepare a composite positive electrode using the above positive electrode material.

[0097] (4) Assemble a sodium-ion battery (the specific steps are the same as in Example 1).

[0098] (5) Test the performance of the sodium-ion battery (the specific steps are the same as in Example 1).

[0099] Example 5

[0100] (1) Prepare the original positive electrode material (the specific steps are the same as in Example 1).

[0101] (2) Set the stirring temperature to 80 °C, and the remaining steps are the same as in Example 1.

[0102] (3) Prepare a composite positive electrode using the above positive electrode material.

[0103] (4) Assemble a sodium-ion battery (the specific steps are the same as in Example 1).

[0104] (5) Test the performance of the sodium-ion battery (the specific steps are the same as in Example 1).

[0105] Example 6

[0106] (1) Prepare the original positive electrode material (the specific steps are the same as in Example 1).

[0107] (2) Set the stirring time to 3 hours, and the remaining steps are the same as in Example 1. (3) Prepare a composite positive electrode using the above positive electrode material.

[0108] (4) Assemble a sodium-ion battery (the specific steps are the same as in Example 1).

[0109] (5) Test the performance of the sodium-ion battery (the specific steps are the same as in Example 1).

[0110] Example 7

[0111] (1) Prepare the original cathode material (the specific steps are the same as those in Example 1).

[0112] (2) Set the stirring time to 6 hours, and the remaining steps are the same as those in Example 1. (3) Prepare the composite cathode using the above cathode material.

[0113] (4) Assemble the sodium-ion battery (the specific steps are the same as those in Example 1).

[0114] (5) Test the performance of the sodium-ion battery (the specific steps are the same as those in Example 1).

[0115] Example 8

[0116] (1) Prepare the original cathode material (the specific steps are the same as those in Example 1).

[0117] (2) Set the stirring time to 24 hours, and the remaining steps are the same as those in Example 1. (3) Prepare the composite cathode using the above cathode material.

[0118] (4) Assemble the sodium-ion battery (the specific steps are the same as those in Example 1).

[0119] (5) Test the performance of the sodium-ion battery (the specific steps are the same as those in Example 1).

[0120] Example 9

[0121] (1) Prepare the original cathode material (the specific steps are the same as those in Example 1).

[0122] (2) Set the heat treatment temperature to 350 °C, and the remaining steps are the same as those in Example 1.

[0123] (3) Prepare the composite cathode using the above cathode material.

[0124] (4) Assemble the sodium-ion battery (the specific steps are the same as those in Example 1).

[0125] (5) Test the performance of the sodium-ion battery (the specific steps are the same as those in Example 1).

[0126] Example 10

[0127] (1) Prepare the original cathode material (the specific steps are the same as those in Example 1).

[0128] (2) Set the heat treatment temperature to 650 °C, and the remaining steps are the same as those in Example 1.

[0129] (3) Prepare the composite cathode using the above cathode material.

[0130] (4) Assemble the sodium-ion battery (the specific steps are the same as those in Example 1).

[0131] (V) Performance test of sodium-ion battery (the specific steps are the same as those in Example 1).

[0132] Example 11

[0133] (I) Prepare the original cathode material (the specific steps are the same as those in Example 1).

[0134] (II) Set the heat treatment temperature to 800 °C, and the other steps are the same as those in Example 1.

[0135] (III) Prepare the composite cathode using the above cathode material.

[0136] (IV) Assembly of sodium-ion battery (the specific steps are the same as those in Example 1).

[0137] (V) Performance test of sodium-ion battery (the specific steps are the same as those in Example 1).

[0138] Example 12

[0139] (I) Prepare the original cathode material (the specific steps are the same as those in Example 1).

[0140] (II) Set the heat treatment temperature to 950 °C, and the other steps are the same as those in Example 1.

[0141] (III) Prepare the composite cathode using the above cathode material.

[0142] (IV) Assembly of sodium-ion battery (the specific steps are the same as those in Example 1).

[0143] (V) Performance test of sodium-ion battery (the specific steps are the same as those in Example 1).

[0144] Table 1 Test results of long-term cycling performance of the batteries in Examples 1-14 and Comparative Examples 1-2

[0145]

[0146]

[0147] It can be seen from the above results and the attached drawings that the original material has poor cycling performance. After being activated at 0.1C for three cycles, the capacity retention rate is 74.01% after cycling 100 times at 1C, and the capacity retention rate is only 32.01% after cycling 400 times. From Figure 4 it can be known that at a high rate of 10C, its specific capacity is lower than 40 mAh / g, and the rate performance is poor. Comparing Examples 1-12 and Comparative Examples 1-4 in the above table, it can be seen that after modification under different conditions, the performance of the modified material fluctuates greatly. When the modification reagent is ethylene glycol, the stirring temperature is 60 °C, the stirring time is 12 hours, and the heat treatment temperature is 500 °C, the performance of the modified material is the best. Figure 4 and Figure 8The comparison shows that even at a high rate of 10C, the specific capacity of the modified material is still greater than 95 mAh / g, and the rate performance has also been significantly improved. In addition, Example 1 and Comparative Example 2 in the above table show that the heat treatment after stirring is an important step in the present invention. If only the solution stirring treatment is carried out without subsequent heat treatment, the cycling performance of the material is still very poor, and the capacity retention rate after 400 cycles is only 37.81%. That is, the subsequent heat treatment can play a role in surface remodeling, thereby constructing a stable interface.

[0148] In summary, the present invention aims at the layered transition metal oxide cathode material NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O 2 for sodium ion batteries, and proposes a simple and effective modification method, that is, heat stirring in ethylene glycol solution followed by heat treatment. The results of multiple comparative experiments and microstructure analysis show that when the material is dissolved in ethylene glycol and continuously stirred at 60°C for 12 hours, and then heat treated at 500°C, the modified material exhibits the best electrochemical characteristics. This process not only enhances the cycling stability of the material, but also improves its rate performance, enabling the battery to maintain high performance at different charge and discharge rates.

[0149] The above description of the embodiments is to enable those of ordinary skill in the art to understand and use the invention. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative labor. Therefore, the present invention is not limited to the above embodiments, and all improvements and modifications made by those skilled in the art without departing from the scope of the present invention should be within the protection scope of the present invention.

Claims

1. A method for modifying a sodium layered transition metal oxide positive electrode material, characterized in that: The layered oxide positive electrode material NFM with an O3 type structure is dissolved in a modified solvent, heated and stirred, and then filtered and dried, and then heat-treated to obtain a modified positive electrode material powder.

2. The method for modifying a sodium layered transition metal oxide positive electrode material according to claim 1, characterized in that: The modified solvent is ethylene glycol or polyethylene glycol.

3. The method for modifying a sodium-electrode layered transition metal oxide positive electrode material according to claim 2, characterized in that: The modified solvent is ethylene glycol.

4. The method for modifying a sodium layered transition metal oxide positive electrode material according to claim 1, characterized in that: The ratio of the added amount of the layered oxide positive electrode material NFM to the modified solvent is 1 g: (4-6) mL.

5. The method for modifying a sodium layered transition metal oxide positive electrode material according to claim 1, characterized in that: The heating and stirring temperature is 40 to 80°C and the time is 6 to 24 hours.

6. The method for modifying a sodium layered transition metal oxide positive electrode material according to claim 1, characterized in that: The drying process is: drying at 80-120°C overnight.

7. The method for modifying a sodium-electrode layered transition metal oxide positive electrode material according to claim 1, characterized in that: The temperature of the heat treatment is 400-650°C.

8. The method for modifying a sodium layered transition metal oxide positive electrode material according to claim 1, characterized in that: The heat treatment time is 4 to 8 hours.

9. A sodium layered transition metal oxide positive electrode material, obtained by the modification method according to any one of claims 1 to 8.

10. Use of the sodium-ion layered transition metal oxide positive electrode material as claimed in claim 9 in constructing a sodium-ion battery with excellent cycle performance and rate performance.

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