A surface reconstruction method of a p2-type sodium ion layered oxide positive electrode material

Abstract

The application provides a surface reconstruction method of a P2 type sodium ion layered oxide positive electrode material, which comprises the following steps: dispersing a sodium source, a manganese source, an iron source and a lithium source in a solvent, performing ball milling treatment and removing the solvent to obtain a precursor powder; and then performing a first calcination treatment, water washing treatment, suction filtration, drying and a second calcination in sequence to obtain a final positive electrode material; wherein the water washing liquid for the water washing treatment is composed of a 0.5 mol / L carbonate buffer, anhydrous ethanol and deionized water, and the volume ratio of the ethanol to the 0.5 mol / L carbonate buffer is (4-6):1. + The application effectively removes the residual alkali on the surface of the sodium ion battery positive electrode material through water washing to realize surface reconstruction, avoids damage to the bulk structure, reduces Na + Loss, improves Na + Transport kinetics, induces surface reconstruction of the layered oxide positive electrode material, forms a disordered sodium-rich interface layer, and effectively improves the electrochemical performance and material structure stability.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery technology, specifically relating to a surface reconstruction method for a P2-type sodium-ion layered oxide cathode material. Background Technology

[0002] During the preparation and storage of layered oxide cathode materials, the instability of air can easily lead to the formation of residual alkaline compounds (mainly sodium carbonate and sodium hydroxide) on the material surface. The formation mechanism can be attributed to three aspects: the re-enrichment of volatile sodium components on the surface during calcination and cooling, uneven reaction of raw material components, and interfacial reactions with humid air. Simultaneously, the presence of residual alkali significantly degrades material performance: on the one hand, strongly alkaline residual alkali easily triggers side reactions at the electrode-electrolyte interface, leading to abnormal thickening or structural instability of the SEI film (solid electrolyte interphase); on the other hand, the strong hygroscopicity of residual alkali exacerbates water absorption, further damaging its crystal structure integrity. Ultimately, this manifests as decreased cycle stability, reduced capacity retention, and other electrochemical performance degradation.

[0003] Currently, most layered oxide cathode materials suffer from poor air stability and water resistance, which can easily lead to significant phase structure evolution (such as changes in interlayer spacing and the formation of impurity phases), increasing ion transport impedance and thus impairing the intrinsic properties of the material.

[0004] In the prior art, high-temperature calcination is considered to repair the damage caused by phase structure evolution to a certain extent. For example, the invention patent with publication number CN121583908A discloses a surface-reconstructed layered oxide cathode material and its preparation method, application and battery, including the following steps: (1) forming carbonate in situ on the surface of the layered oxide cathode material to obtain a surface-activated layered oxide cathode material; (2) after the surface-activated layered oxide cathode material is subjected to an ion exchange reaction with a metal salt, it is then subjected to annealing treatment to obtain the surface-reconstructed layered oxide cathode material.

[0005] For example, the invention patent with publication number CN119381439A discloses a layered oxide cathode material for sodium-ion batteries based on surface reconstruction, its preparation method and application. The cathode material is prepared by the following steps: (1) Sodium source, lithium source, manganese dioxide and oxides of any one of Al, Fe and Ni are prepared according to the chemical formula Na 0.71 Li 0.2 M x Mn 0.8-xThe molar ratio of each element in O2 is weighed, and the sodium source is in excess by 3%-5% based on sodium element. After mixing, the mixture is dry ball-milled for 5-10 h to obtain the precursor; (2) The precursor obtained in step (1) is first calcined at 300℃-500℃ for 1-3 h, and then calcined at 900℃-1000℃ for 8-12 h to obtain the layered oxide cathode material body; (3) The layered oxide cathode material body obtained in step (2) is rapidly quenched and placed in a molybdate aqueous solution at room temperature. Then the material is taken out, washed with deionized water, and vacuum dried to obtain the sodium-ion battery layered oxide cathode material based on surface reconstruction. Although high-temperature calcination can repair structural damage to a certain extent, it will aggravate the loss of sodium source volatilization and significantly increase energy consumption and cost.

[0006] Therefore, efficiently removing surface residual alkali and simultaneously improving electrochemical performance without damaging the bulk structure is an important research direction. Solving this problem will not only help deepen our understanding of the air stability mechanism of layered oxide cathode materials, but also provide key technical support for the large-scale application of layered oxide cathode materials. Summary of the Invention

[0007] In order to effectively remove residual alkali without damaging the bulk structure, this invention provides a surface reconstruction method for P2 type sodium ion layered oxide cathode material. The method uses water washing to remove residual alkali from the material surface and forms a disordered sodium-rich layer in situ, which effectively improves electrochemical performance and material structural stability.

[0008] The technical solution adopted by this application to solve the above problems is as follows: This invention provides a surface reconstruction method for a P2-type sodium ion layered oxide cathode material, comprising the following steps: (1) Disperse sodium source, manganese source, iron source and lithium source in solvent to obtain solid-liquid mixture; (2) The solid-liquid mixture is ball-milled to obtain a precursor slurry, and then the solvent is removed to obtain a precursor powder; (3) The precursor powder is subjected to a single calcination treatment to obtain the material after single calcination; (4) The material after the first calcination is washed with water, and then filtered, dried and calcined again to obtain the final P2 type sodium ion layered oxide cathode material. The water washing solution is composed of 0.5 mol / L carbonate buffer, ethanol and deionized water, and the volume ratio of ethanol to 0.5 mol / L carbonate buffer is (4~6):1.

[0009] This invention abandons the traditional high-temperature calcination surface reconstruction method and adopts surface water washing to effectively remove residual alkali without damaging the bulk structure.

[0010] Specifically, a carbonate buffer solution with a total carbonate concentration of 0.5 mol / L was selected as the main component of the washing solution, and HCO3 was used as the washing solution. - / CO3 2- The buffer solution gently removes residual alkaline substances (sodium hydroxide, sodium carbonate) from the surface. The buffer solution disrupts the hydrogen bonding between the residual alkaline substances and the material surface. Adding ethanol to a carbonate buffer solution lowers the dielectric constant of the system and promotes CO32--. 2- Hydrolysis (hydrolysis reaction formula: CO3) 2- +H2O⇌HCO3 - +OH - This process disrupts the hydrogen bond adsorption between residual alkaline substances (NaOH, Na2CO3) and the material surface, and increases the solubility of the residual alkaline substances. The bicarbonate produced by hydrolysis can neutralize the free OH groups released from the residual alkaline substances on the cathode material surface. - This promotes the desorption of residual alkaline substances and makes them more easily soluble in aqueous buffer solutions. Therefore, washing sodium ion layered oxide cathode materials with a carbonate buffer solution of the above specifications can effectively remove residual alkali from the material surface without damaging the bulk structure and reducing Na+ ion concentration. + Loss, increase Na + Transport kinetics. Inducing surface reconstruction of layered oxide cathode materials to form a sodium-rich layer with disordered interfaces effectively improves the electrochemical performance of layered oxide cathode materials.

[0011] Preferably, the sodium source in step (1) is selected from at least one of sodium carbonate, sodium bicarbonate, and sodium acetate; The manganese source is selected from at least one of manganese dioxide and manganese oxide; The iron source is selected from at least one of iron oxide and iron(III) oxide; The lithium source is selected from at least one of lithium hydroxide, lithium acetate, and lithium carbonate.

[0012] More preferably, according to the chemical formula Na 0.7 Li 0.2 Mn 0.7 Fe 0.1 The molar ratio of each element in O2 is determined by weighing out sodium, manganese, iron, and lithium sources, with sodium source added in excess by 5% (based on sodium elemental content) and lithium source added in excess by 2% (based on lithium elemental content). This excess addition is to compensate for losses during the high-temperature sintering process.

[0013] Preferably, the solvent in step (2) is at least one of anhydrous ethanol, acetone, and methanol.

[0014] Preferably, in step (2), the ball-to-material ratio during ball milling is 10:1, the ball milling speed is 300 rpm, and the ball milling time is 5 h.

[0015] Optionally, in step (2), after the precursor slurry is dried at 60-80°C, it is filtered through a 300-500 mesh grading sieve to obtain precursor powder.

[0016] Preferably, in step (3), the heating and cooling rate during the first calcination is 2-5 ℃ / min, the first calcination temperature is 900℃-1000℃, and the first calcination time is 10-16 h.

[0017] Preferably, the preparation process of the washing solution in step (4) includes: first mixing 0.5 mol / L carbonate buffer with deionized water, and then adding ethanol; wherein the volume ratio of ethanol to deionized water is 1:1.

[0018] Mixing carbonate buffer with deionized water first, and then adding ethanol, can effectively prevent salt precipitation caused by excessively high local ethanol concentration.

[0019] Preferably, the pH of the 0.5 mol / L carbonate buffer solution in step (4) is 9-10.

[0020] Preferably, the pH of the washing solution in step (4) is 10.5-11.5.

[0021] Preferably, the product after filtration in step (4) is dried in a vacuum environment at 60℃-80℃ for 8-12 h.

[0022] Preferably, in step (4), the heating and cooling rate of the secondary calcination is 2-5 ℃ / min, the temperature of the secondary calcination is 900℃-1000℃, and the secondary calcination time is 6-8 h.

[0023] Compared with the prior art, the present invention has the following beneficial effects: Using a diluted carbonate buffer solution as a washing solution to wash sodium-ion battery layered oxide cathode materials can efficiently remove residual sodium compounds (mainly sodium carbonate and sodium hydroxide) from the material surface, reducing interfacial side reactions caused by residual alkali at the source, inhibiting CO2 release during cycling, and significantly improving electrode interface stability. Reducing direct contact between the active material and the electrolyte induces the formation of a thin, dense, and stable cathode-electrolyte interfacial film, improving sodium ion transport kinetics and interfacial compatibility. After washing, the cathode material surface undergoes reconstruction, with a sodium-rich disordered layer forming in situ, further enhancing the performance of sodium-ion battery layered oxide cathode materials and providing a simple, efficient, and universally applicable strategy for their large-scale preparation. Attached Figure Description

[0024] Figure 1 The images show scanning electron microscope (SEM) results of the sodium-ion battery cathode materials prepared in Example 1 and Comparative Example 1; where, Figure 1 Figure a in the middle and Figure 1Figure b in the diagram is the SEM image of Comparative Example 1. Figure 1 Figure c in the middle and Figure 1 The d-image in the figure is the SEM image of Example 1.

[0025] Figure 2 The X-ray diffraction (XRD) results are shown for the sodium-ion battery cathode materials prepared in Example 1 and Comparative Example 1; wherein, Figure 2 Figure a in the figure is the XRD pattern of Example 1 and Comparative Example 1. Figure 2 Figure b in the figure shows the XRD patterns of Example 1 and Comparative Example 1 in the range of 15°-17°.

[0026] Figure 3 The images show transmission electron microscopy (TEM) results of the sodium-ion battery cathode materials prepared in Example 1 and Comparative Example 1; where, Figure 3 Figure a in the diagram is the TEM image of Comparative Example 1. Figure 3 Figure b in the image is a TEM image of Example 1. Figure 3 Image c in the image is a TEM image that is further magnified from image b.

[0027] Figure 4 The X-ray photoelectron spectroscopy (XPS) spectra of the sodium-ion battery cathode materials prepared in Example 1 and Comparative Example 1 are shown below; Figure 4 Figure a in the diagram is the XPS plot of Comparative Example 1. Figure 4 Figure b in the figure is the XPS diagram of Example 1.

[0028] Figure 5 The first charge-discharge curves of the sodium-ion battery cathode materials prepared in Example 1 and Comparative Examples 1-3 are shown at a current density of 0.2 C.

[0029] Figure 6 The graph shows the rate performance of the sodium-ion battery cathode materials prepared in Example 1 and Comparative Examples 1-3.

[0030] Figure 7 The graph shows the cycle performance of the sodium-ion battery cathode materials prepared in Example 1 and Comparative Examples 1-3 at a current density of 0.2 C. Detailed Implementation

[0031] The specific embodiments of this application will be further described in detail below with reference to the accompanying drawings and examples. Unless otherwise specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all commercially available products. The specific embodiments of this application will be further described in detail below with reference to the accompanying drawings and examples.

[0032] The raw materials used in the following examples and comparative examples were all purchased from the market.

[0033] Example 1 Sodium-ion battery cathode material Na 0.7 Li 0.2 Mn 0.7 Fe 0.1 The method for preparing O2 involves solid-state sintering, followed by water washing of the P2-type sodium-ion battery layered oxide cathode material with a diluted 551 carbonate buffer solution, and includes the following steps: (1) Weigh 0.35 mol sodium carbonate, 0.1 mol lithium carbonate, 0.7 mol manganese dioxide and 0.05 mol ferric oxide into a 50 mL zirconium dioxide ball mill jar according to the chemical formula stoichiometry, wherein sodium carbonate and lithium carbonate are in excess by 5 mol% and 2 mol% respectively. Disperse them in 30 mL acetone solvent to obtain a solid-liquid mixture.

[0034] (2) The solid-liquid mixture was ball-milled with a ball-to-material ratio of 10:1, a rotation speed of 300 rpm, and an effective ball-milling time of 5 h to obtain a precursor slurry. The precursor slurry was placed in an oven and dried at 60℃-80℃ to remove acetone. Then, it was fully crushed and ground in a mortar and sieved through a 400-mesh grading sieve to obtain precursor powder.

[0035] (3) The precursor powder was placed in a tube furnace for a first calcination. Under an air atmosphere, the tube furnace was heated from room temperature to 960°C at a rate of 5°C / min and held for 960 min. Then it was cooled to 300°C at a rate of 2°C / min and allowed to cool naturally. The material after the first calcination was obtained and named NLMFO.

[0036] (4) Prepare a diluted 551 carbonate buffer solution as a washing solution according to the ratio of ethanol:water:buffer solution = 5:5:1. Mix 30 mL of ethanol, 30 mL of deionized water and 6 mL of 0.5 mol / L carbonate buffer solution (0.5 CBS) evenly.

[0037] Take 30 mL of the diluted carbonate buffer solution to wash the positive electrode material NLMFO: Select 0.5 g of positive electrode material NLMFO and place it in a beaker. Add 30 mL of the diluted carbonate buffer solution and stir magnetically for 30 min. Then filter it. The filtered product is dried in a vacuum environment at 60℃-80℃ for 8-12 h.

[0038] The dried filter paste was calcined a second time and placed in a tube furnace. Under an air atmosphere, the tube furnace was heated from room temperature to 960°C at a rate of 5°C / min and held at that temperature for 480 min. Then, it was cooled to 300°C at a rate of 2°C / min and allowed to cool naturally to room temperature, thus obtaining the sodium-ion battery layered oxide cathode material DAE washed-551.

[0039] Battery assembly: The positive electrode material DAE washed-551 prepared in Example 1 was weighed and mixed with Super-P and polyvinylidene fluoride at a mass ratio of 7:2:1. Simultaneously, an appropriate amount of the positive electrode solvent N-methylpyrrolidone was added to prepare a positive electrode slurry. The positive electrode slurry was then mixed at a concentration of 1.5-3 mg / cm³. 2 The coating was applied to an aluminum foil current collector and dried in an oven at 110 °C for 12 h to obtain a positive electrode. Using the prepared positive electrode, cut to a diameter of 12 mm, as the positive electrode, metallic sodium as the negative electrode, and glass fiber as the separator, a button half-cell was prepared in an argon glove box using 1 mol / L NaClO4 EC / PC + 5F%FEC as the electrolyte.

[0040] Example 2 The process in Example 2 is the same as in Example 1, except that the P2 type sodium-ion battery layered oxide cathode material is washed with water using the diluted 641 carbonate buffer solution. Specifically, the diluted carbonate buffer solution is prepared according to the ratio of ethanol:water:buffer solution = 6:4:1 as the washing solution. 36 mL of ethanol, 24 mL of deionized water, and 6 mL of 0.5 mol / L carbonate buffer solution (0.5 CBS) are mixed evenly to obtain the solution.

[0041] Take 30 mL of the diluted 641 carbonate buffer solution to wash the positive electrode material NLMFO: Select 0.5 g of positive electrode material NLMFO and place it in a beaker, add 30 mL of diluted carbonate buffer solution and stir magnetically for 30 min, then filter it, and dry the filtered product in a vacuum environment of 60℃-80℃ for 8-12 h.

[0042] The dried filter paste was calcined a second time and placed in a tube furnace. Under an air atmosphere, the tube furnace was heated from room temperature to 900°C at a rate of 5°C / min and held at that temperature for 480 min. Then, it was cooled to 300°C at a rate of 2°C / min and allowed to cool naturally to room temperature, thus obtaining the sodium-ion battery layered oxide cathode material DAE washed-641.

[0043] Battery assembly: The positive electrode material DAE washed-641 prepared in Example 2 was weighed and mixed with Super-P and polyvinylidene fluoride at a mass ratio of 7:2:1. Simultaneously, an appropriate amount of the positive electrode solvent N-methylpyrrolidone was added to prepare a positive electrode slurry. The positive electrode slurry was then mixed at a concentration of 1.5-3 mg / cm³. 2The coating was applied to an aluminum foil current collector and dried in an oven at 110 °C for 12 h to obtain a positive electrode. Using the prepared positive electrode, cut to a diameter of 12 mm, as the positive electrode, metallic sodium as the negative electrode, and glass fiber as the separator, a button half-cell was prepared in an argon glove box using 1 mol / L NaClO4 EC / PC + 5F%FEC as the electrolyte.

[0044] Comparative Example 1 (without water washing treatment) The process of Comparative Example 1 is the same as that of Example 1, except that the water washing treatment in step (4) of Example 1 is not performed, and the cathode material is directly calcined twice to obtain Unwashed cathode material.

[0045] Battery assembly: Button half-cells were prepared based on the unwashed cathode material prepared in Comparative Example 1.

[0046] Comparative Example 2 Comparative Example 2 is the same as Example 1, except that the water washing solution in step (4) is deionized water, and the positive electrode material DI washed is obtained.

[0047] Comparative Example 3 Comparative Example 3 is the same as Example 1, except that the water washing solution in step (4) is a 0.5 mol / L carbonate buffer solution (0.5 CBS), and the positive electrode material is washed with 0.5 CBS.

[0048] Detection Example 1 The microstructure of the cathode material DAE washed-551 prepared in Example 1 and the cathode material Unwashed prepared in Comparative Example 1 were characterized by scanning electron microscopy. Figure 1 As shown.

[0049] As can be seen from the figure, the obtained cathode material is unwashed ( Figure 1 Figure a in the middle and Figure 1 Figure b in the diagram) and the cathode material DAE washed-551 ( Figure 1 Figure c in the middle and Figure 1 Figure d shows well-crystallized hexagonal particles with a diameter of approximately 2-6 μm. Further scanning electron microscopy revealed that washing with a diluted buffer solution removed residual alkali. The blocky particles, after DAE washing, showed good removal of residual alkali from the material surface, demonstrating superior surface cleanliness compared to those washed under other conditions, effectively removing surface impurities.

[0050] Detection Example 2 The phase structures of the cathode material DAE washed-551 prepared in Example 1, the cathode material Unwashed prepared in Comparative Example 1, and the NLMFO material after one calcination were characterized by X-ray diffraction. Figure 2 As shown.

[0051] pass Figure 2 The XRD test results in Figure a show that all phases retain the P2 phase structure, as shown in Figure a. Figure 2 As shown in Figure b, within the range of 15°-17°, the (002) peak position of the unwashed cathode material shifts downwards, resulting in an increase in the c-axis interlayer spacing. This structural difference makes it easier for moisture to embed into the interlayer of the unwashed cathode material, reducing the material's air stability. During the synthesis process, excess sodium is usually used to compensate for sodium loss during the calcination of the precursor. Due to this excess sodium, residual sodium compounds are left on the surface of the final material.

[0052] Detection Example 3 To further characterize the morphological changes of the surface reconstruction, transmission electron microscopy was used to perform a more detailed characterization of the microstructure of the cathode material DAE washed-551 prepared in Example 1 and the cathode material Unwashed prepared in Comparative Example 1.

[0053] like Figure 3 As shown, Figure 3 Figure a shows the particle surface and bulk structure of the unwashed cathode material. Figure 3 Figure b in the middle - Figure 3 Figure c shows the surface and bulk structure of the cathode material DAE washed-551. As can be seen from the figure, alkaline washing induces structural reconstruction in the 2-5 nm region of the surface layer. Washing with a carbonate buffer solution can form a thin and uniform disordered layer on the surface of the cathode material. After washing, surface reconstruction occurs, and a sodium-rich disordered layer forms in situ on the surface. This disordered layer effectively alleviates interlayer stress during the Na⁺ deintercalation / intercalation process.

[0054] Detection Example 4 like Figure 4 As shown, Figure 4 Figure a in the diagram is the XPS plot of Comparative Example 1. Figure 4 Figure b in the figure is the XPS image of Example 1. XPS characterization further confirms that the surface manganese transition metal element is significantly reduced. This result also proves that the (002) peak position of the unwashed cathode material has shifted to a lower angle. This phenomenon is due to the structural optimization and reconstruction during the washing process, and a sodium-rich disordered layer is formed in situ on the surface after washing. This disordered layer can effectively alleviate the interlayer stress during the Na⁺ deintercalation / intercalation process.

[0055] Case 5 As shown in Table 1, the stoichiometry of the examples and comparative examples was determined by inductively coupled plasma optical emission spectroscopy (ICP-OES).

[0056] Table 1

[0057] As shown in Table 1, the analysis further confirmed that the elemental ratios of the cathode material DAE washed-551 closely matched the stoichiometric ratios of the designed chemical formula. The unwashed cathode material effectively removed residual alkali from its surface through water washing. Its (002) peak exhibited significantly better stability compared to the NLMFO material after a single calcination. The shift of the (002) peak to a higher angle after water washing reflects a slight contraction in the (002) interplanar spacing, and the formation of a disordered sodium-rich layer on the surface effectively improved the performance of the cathode material.

[0058] Case 6 The button half-cells assembled in Example 1 and Comparative Examples 1-3 were subjected to relevant electrochemical tests on the Blue Electricity Test System at a test temperature of 25 °C.

[0059] like Figure 5 As shown, the first discharge specific capacity of the half-cell of Example 1 (cathode material DAE washed-551) at 2-4.3 V and 0.2 C (1C=120 mAh / g) was 136.7 mAh / g; the first discharge specific capacity of the half-cell of Comparative Example 1 (cathode material Unwashed) was 81.8 mAh / g; the first discharge specific capacity of the half-cell of Comparative Example 2 (cathode material DI washed) was 74.4 mAh / g; and the first discharge specific capacity of the half-cell of Comparative Example 3 (cathode material 0.5CBS washed) was 65.7 mAh / g.

[0060] like Figure 6 The rate performance is shown. The half-cell of Comparative Example 1 (with unwashed cathode material) has a discharge specific capacity of 73.7 mAh / g at 5 C. The rate performance results indicate that washing effectively removes residual alkali from the surface, significantly improving the rate performance.

[0061] like Figure 7As shown, the half-cell of Example 1 (cathode material DAE washed-551) exhibited a discharge specific capacity of 114.9 mAh / g after 70 cycles at 0.2 C (1 C = 120 mAh / g); the half-cell of Comparative Example 1 (cathode material unwashed) exhibited a discharge specific capacity of 92 mAh / g after 70 cycles at 0.2 C (1 C = 120 mAh / g); the half-cell of Comparative Example 2 (cathode material 0.5CBS washed) exhibited a discharge specific capacity of 72.7 mAh / g after 70 cycles at 0.2 C (1 C = 120 mAh / g); and the half-cell of Comparative Example 3 (cathode material 0.5CBS washed) exhibited a discharge specific capacity of 69.9 mAh / g after 70 cycles at 0.2 C (1 C = 120 mAh / g). The results indicate that the electrochemical performance and rate capability of the comparative examples are lower than those of Example 1, and the Na content in the corresponding ICP values ​​is significantly reduced.

[0062] In summary, this invention removes residual alkali by washing P2-type layered oxides with water, which effectively removes residual alkaline compounds on the surface and avoids damage to the bulk structure of the material. At the same time, the surface reconstruction forms a disordered sodium-rich layer at the interface, which improves Na+ transport kinetics, reduces interfacial side reactions, and generates higher specific capacity and energy density.

[0063] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A surface reconstruction method for a P2-type sodium-ion layered oxide cathode material, characterized in that, Includes the following steps: (1) Disperse sodium source, manganese source, iron source and lithium source in solvent to obtain solid-liquid mixture; (2) The solid-liquid mixture is ball-milled to obtain a precursor slurry, and then the solvent is removed to obtain a precursor powder; (3) The precursor powder is subjected to a single calcination treatment to obtain the material after single calcination; (4) The material after the first calcination is washed with water, and then filtered, dried and calcined again to obtain the final P2 type sodium ion layered oxide cathode material.

2. The surface reconstruction method for P2-type sodium ion layered oxide cathode material according to claim 1, characterized in that, The washing solution for the water washing process consists of 0.5 mol / L carbonate buffer, anhydrous ethanol and deionized water, with a volume ratio of ethanol to 0.5 mol / L carbonate buffer of (4~6):

1.

3. The surface reconstruction method for P2-type sodium ion layered oxide cathode material according to claim 1, characterized in that, The sodium source in step (1) is selected from at least one of sodium carbonate, sodium bicarbonate, and sodium acetate; The manganese source is selected from at least one of manganese dioxide and manganese oxide; The iron source is selected from at least one of iron oxide and iron(III) oxide; The lithium source is selected from at least one of lithium hydroxide, lithium acetate, and lithium carbonate.

4. The surface reconstruction method for P2-type sodium ion layered oxide cathode material according to claim 2, characterized in that, According to the chemical formula Na 0.7 Li 0.2 Mn 0.7 Fe 0.1 The molar ratio of each element in O2 is determined by weighing out sodium source, manganese source, iron source and lithium source, wherein sodium source is added in excess by 5% based on sodium element and lithium source is added in excess by 2% based on lithium element.

5. The surface reconstruction method for P2-type sodium ion layered oxide cathode material according to claim 1, characterized in that, The solvent in step (2) is at least one of anhydrous ethanol, acetone, and methanol.

6. The surface reconstruction method for P2-type sodium ion layered oxide cathode material according to claim 1, characterized in that, In step (3), the heating and cooling rate during the first calcination is 2-5 ℃ / min, the first calcination temperature is 900℃-1000℃, and the first calcination time is 10-16 h.

7. The surface reconstruction method for the P2-type sodium ion layered oxide cathode material according to claim 1, characterized in that, The preparation process of the washing solution in step (4) includes: first mixing 0.5 mol / L carbonate buffer with deionized water, and then adding ethanol; wherein the volume ratio of ethanol to deionized water is 1:

1.

8. The surface reconstruction method for P2-type sodium-ion layered oxide cathode material according to claim 1, characterized in that, The pH of the washing solution in step (4) is 10.5-11.

5.

9. The surface reconstruction method for the P2-type sodium ion layered oxide cathode material according to claim 1, characterized in that, The product after filtration in step (4) is dried in a vacuum environment at 60℃-80℃ for 8-12 h.

10. The surface reconstruction method for the P2-type sodium ion layered oxide cathode material according to claim 1, characterized in that, In step (4), the heating and cooling rate of the secondary calcination is 2-5 ℃ / min, the temperature of the secondary calcination is 900℃-1000℃, and the secondary calcination time is 6-8 h.

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