Sodium-ion battery positive electrode material, preparation method and application

Abstract

The invention relates to a sodium-ion battery positive electrode material, a preparation method and application, and relates to the technical field of sodium-ion battery positive electrode materials. The preparation method of the sodium ion battery positive electrode material comprises the following steps: obtaining NFMO; mixing the NFMO with the precursor to obtain a first mixture; wherein the mass ratio of the precursor to the NFMO is (0-5): 100, and the precursor comprises lithium carbonate and tin fluoride; ball-milling the first mixture to obtain a second mixture; and performing high-temperature treatment on the second mixture to obtain the modified sodium-ion battery positive electrode material. According to the preparation method, the bulk phase structure and the interface stability of the P2 type oxide can be synchronously optimized, it is ensured that the process is simple, large-scale production can be achieved, the positive electrode material obtained through the preparation method is used for preparing a sodium ion battery, and the energy density and the cycling stability of sodium ions can be remarkably improved.

Description

Technical Field

[0001] The present application relates to the technical field of sodium ion battery positive electrode materials, and in particular to a sodium ion battery positive electrode material, a preparation method and an application thereof. Background Art

[0002] As the global demand for renewable energy and efficient energy storage systems continues to escalate, sodium-ion batteries (SIBs) have become a promising alternative to lithium-ion batteries due to their low cost, resource abundance, and environmental sustainability. Despite these advantages, SIBs still face challenges in achieving competitive energy density and cycling stability, which are crucial for their widespread adoption in large-scale energy storage applications. As the core component of SIBs, the cathode material plays a key role in determining the overall performance of the battery.

[0003] Therefore, the development of high-performance cathode materials has become the core focus of current research. 0.67 Fe 0.5 Mn 0.5 O2 (NFMO) has attracted widespread attention due to its high specific capacity (260 mAh / g), low cost, and ease of synthesis. However, NFMO cathode materials suffer from several inherent limitations, including structural instability during cycling, interfacial side reactions, and capacity degradation under high voltage. These issues have severely hindered their practical application in high-performance SIBs.

[0004] In response to the key issues of P2-type layered oxide cathode materials, researchers have explored a variety of modification strategies. In terms of element doping, by introducing Mg 2+ 、Al 3+ 、Ti 4+ Isocation or F - 、S 2- Anions such as Na + interlayer spacing and suppress the P2-O2 phase transition.

[0005] However, these single doping strategies have obvious limitations:

[0006] First, it is difficult to optimize Na + Diffusion kinetics (such as Mg 2+ Although doping improves ionic conductivity, it cannot suppress Jahn-Teller distortion) and structural stability (thermodynamics);

[0007] Secondly, specific doping can introduce side effects, such as Al 3+ The strong Al-O bond leads to electron localization, which significantly reduces the electronic conductivity of the material. 4+ Doping may induce irreversible oxygen vacancy formation, resulting in capacity decay.

[0008] In terms of surface coating modification, the use of oxides such as AlO and TiO can reduce the dissolution of transition metals (such as Mn 2+ Dissolution can be reduced by 50%), but this presents new challenges: On the one hand, the insulating coating significantly increases interfacial charge transfer impedance, especially under high-rate conditions; on the other hand, the coating obtained by traditional mechanical mixing methods suffers from weak bonding and uneven coverage, and is prone to delamination during long-term cycling, exposing fresh active surfaces and triggering persistent side reactions. These limitations severely restrict the practical application of a single modification strategy.

[0009] Therefore, developing a preparation method that can simultaneously optimize the bulk structure and interface stability of P2-type oxides and ensure that its process is simple and can be produced on a large scale is the key to solving the problems of capacity attenuation and insufficient cycle performance of sodium-ion battery positive electrode materials. Summary of the Invention

[0010] In view of the shortcomings of the existing technology, the present application provides a P2 type sodium ion battery positive electrode material modified by tin doping and lithium fluoride coating, a preparation method and application. The preparation method uses lithium carbonate (Li2CO3), tin fluoride (SnF2) and . NFMO was used as the main raw material and ball milled in different proportions and then calcined at high temperature to obtain a modified sodium ion battery cathode material; wherein, Sn 4+ Ions replace transition metal sites, which can effectively expand the lattice spacing and reduce Na + Diffusion energy barrier, improve the diffusion coefficient; at the same time, Sn 4+ The high valence characteristics of LiF can inhibit the Jahn-Teller effect, stabilize the crystal structure, and reduce the phase change damage during the cycle. The LiF coating layer has excellent chemical stability and ionic conductivity, which can effectively block the corrosion of the electrolyte on the positive electrode material and maintain rapid Na + Interface transport. Through the synergistic effect of Sn doping and LiF coating, Sn 4+ Optimizing the bulk structure provides stable Na + The modified cathode material exhibits a high reversible specific capacity of 158.2 mAh / g (0.5C) in the voltage range of 1.5-4.2 V, and a capacity retention rate of 39.87% after 200 cycles at a rate of 1C, which is significantly improved compared with the capacity retention rate of the raw material (23.19%). At the same time, it can still maintain an excellent rate performance of 78.1 mAh / g at a high rate of 5C, which significantly improves the energy density and cycle stability of sodium-ion batteries.

[0011] To achieve the above objectives, this application provides the following technical solutions:

[0012] In a first aspect, the present application provides a method for preparing a P2-type sodium ion battery positive electrode material synergistically modified by tin doping and lithium fluoride coating, which comprises the following steps:

[0013] Get NFMO;

[0014] Mixing NFMO with a precursor to obtain a first mixture; wherein the mass ratio of the precursor to the NFMO is 0 to 5:100, and the precursor includes lithium carbonate and tin fluoride;

[0015] ball milling the first mixture to obtain a second mixture;

[0016] The second mixture is subjected to high-temperature treatment to obtain a modified sodium ion battery positive electrode material.

[0017] Furthermore, the mass ratio of the precursor to the NFMO is 1 to 5:100.

[0018] Furthermore, the molar mass ratio of the lithium carbonate to the tin fluoride is 1:1.5 to 2.5.

[0019] Furthermore, the time for ball milling the first mixture is set to 3 to 5 hours.

[0020] Furthermore, when the second mixture is subjected to high-temperature treatment, the treatment temperature is set to 650-750° C., and the treatment time is set to 5-7 hours.

[0021] Furthermore, obtaining the NFMO includes the following steps:

[0022] Dissolving NaNO3, Fe(NO3)3·9H2O and Mn(CH3COO)2·4H2O in deionized water to obtain a first solution;

[0023] continuously stirring the first solution and adding the citric acid solution to the first solution to obtain a second solution;

[0024] removing water from the second solution to obtain a gel-like primary product;

[0025] The primary product is finely ground and calcined to obtain NFMO.

[0026] Furthermore, the molar ratio of total metal ions to citric acid in the second solution is maintained at 1:0.8 to 1:2.

[0027] Furthermore, the calcining of the primary product comprises the following steps: pre-calcining at 400-500° C. for 3-5 hours, and final calcining at 850-950° C. for 9-12 hours.

[0028] In a second aspect, the present application provides a sodium ion battery positive electrode material, which is prepared by the aforementioned preparation method.

[0029] In a third aspect, the present application provides the use of the aforementioned sodium ion battery positive electrode material in the preparation of a sodium ion battery.

[0030] This application provides a P2-type sodium ion battery positive electrode material modified by synergistic modification of tin doping and lithium fluoride coating, a preparation method, and applications. Compared with the existing technology, it has at least the following advantages:

[0031] 1. By doping Sn 4+ Ions replace transition metal sites, which can effectively expand the lattice spacing and significantly reduce the Na + Diffusion energy barrier, improve its diffusion coefficient; at the same time, Sn 4+ The high valence state of the material can stabilize the crystal structure, inhibit phase change damage during the cycle, and greatly improve the structural stability of the material.

[0032] 2. The LiF coating layer has excellent chemical stability and ionic conductivity, which can effectively block electrolyte corrosion, reduce the amount of transition metal dissolution, and maintain rapid Na + Interface transmission significantly improves the interface stability of the material.

[0033] 3. This application innovatively uses SnF2 and Li2CO3 as precursors, and simultaneously achieves Sn doping and LiF coating through a one-step calcination method. The process is simple, low-cost and easy to scale up. The modified positive electrode material obtained by this method exhibits a high reversible specific capacity of 158.2 mAh / g in the voltage range of 1.5-4.2 V (0.5C), and a capacity retention rate of 39.8% after 200 cycles. At the same time, it still maintains excellent performance of 78.1 mAh / g at a high rate of 5C, providing a new technical solution for the development of high-performance sodium-ion batteries. In addition, this method is simple to operate, has good stability, and can be produced on a large scale. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 Schematic diagram of the preparation process of the P2 type sodium ion battery positive electrode material prepared by synergistic modification of tin doping and lithium fluoride coating in the embodiment of the present application.

[0035] Figure 2 XRD comparison charts of 0% NFMO, 1% NFMO, 3% NFMO, 5% NFMO and NFMO positive electrode materials prepared in the examples and comparative examples of the present application.

[0036] Figure 3 These are SEM images of 3% NFMO prepared in Example 3 of the present application and NFMO prepared in the comparative example.

[0037] Figure 4 TEM and EDS spectra of 3% NFMO prepared in Example 3 of the present application and NFMO prepared in the comparative example, respectively.

[0038] Figure 5 This is the XPS total spectrum of 3% NFMO prepared in Example 3 of the present application.

[0039] Figure 6 This is the F1s single peak spectrum in the XPS spectrum of 3% NFMO prepared in Example 3 of this application

[0040] Figure 7 This is a comparison chart of the rate performance of sodium ion batteries assembled with 0% NFMO, 1% NFMO, 3% NFMO and 5% NFMO prepared in the examples and comparative examples of the present application and NFMO.

[0041] Figure 8 This is a comparison chart of the cycling performance of sodium ion batteries assembled with 0% NFMO, 1% NFMO, 3% NFMO and 5% NFMO prepared in the examples and comparative examples of the present application.

[0042] Figure 9 CV curves of 3% NFMO prepared in Example 3 of the present application and NFMO prepared in the comparative example at a scan rate of 0.1 mv / s.

[0043] Figure 10 GITT curves of 3% NFMO prepared in Example 3 of the present application and NFMO prepared in the comparative example. DETAILED DESCRIPTION

[0044] In order to make the purpose, technical solutions and advantages of this application more clear, the following further describes this application in detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0045] The present application provides a synergistic modification method for a P2-type layered oxide cathode material for sodium-ion batteries. The method simultaneously achieves tin doping and in-situ formation of a lithium fluoride coating layer through ball milling and a one-step calcination process. While maintaining the high specific capacity of the material, the structural stability and interface stability are significantly improved, so that the modified cathode material has both excellent cycle performance and rate performance.

[0046] A method for preparing a positive electrode material for a sodium ion battery, referring to Figure 1 , including the following steps:

[0047] S1. Obtain NFMO;

[0048] In a specific embodiment, obtaining the NFMO includes the following steps:

[0049] S11, dissolving NaNO3, Fe(NO3)3·9H2O and Mn(CH3COO)2·4H2O in deionized water to obtain a first solution;

[0050] The ratios of the specific components within NFMO can be achieved by adjusting the components of the above three raw materials, and the ratios of the above three raw materials are specifically set according to actual conditions.

[0051] S12, continuously stirring the first solution, and adding citric acid solution to the first solution to obtain a second solution;

[0052] In a specific embodiment, the molar ratio of total metal ions to citric acid in the second solution is maintained at 1:0.8 to 1:2. For example, it can be maintained at 1:0.8, 1:1, or 1:1.2.

[0053] S13, removing water from the second solution to obtain a gel-like primary product;

[0054] In a specific embodiment, S13 specifically includes the following steps:

[0055] S131. Heat the second solution until no liquid remains on the surface to obtain a crude product; wherein the heating temperature is set to 55-65°C.

[0056] S132, heating the crude product to obtain a primary product; wherein the heating temperature is set to 75-85° C., and the heating time is set to 12 h.

[0057] S14, finely grinding and calcining the primary product to obtain NFMO.

[0058] In a specific embodiment, calcining the primary product comprises the following steps: pre-calcining at 400-500° C. for 3-5 hours, and final calcining at 850-950° C. for 9-12 hours.

[0059] S2. Mixing NFMO with a precursor to obtain a first mixture; wherein the mass ratio of the precursor to NFMO is 0 to 5:100, and the precursor includes lithium carbonate and tin fluoride.

[0060] Preferably, in a specific embodiment, the mass ratio of the precursor to NFMO is 1 to 5:100; further preferably, in another specific embodiment, the mass ratio of the precursor to NFMO is 3:100.

[0061] In a specific embodiment, the molar mass ratio of lithium carbonate to tin fluoride is 1:1.5-2.5.

[0062] S3. Ball milling the first mixture to obtain a second mixture.

[0063] The ball milling time of the first mixture is set to 3 to 5 hours. The ball milling time can be adjusted according to actual conditions, for example, it can be set to 3 hours, 4 hours or 5 hours to ensure that the first mixture is fully ball milled.

[0064] Furthermore, the specific method of ball milling can also be specifically configured. For example, in one embodiment, the first mixture can be ball milled continuously for a set time using either a forward or counter-rotating ball milling method. In another embodiment, the first mixture can be ball milled continuously for a set time using an alternating method of forward and counter-rotating ball milling.

[0065] Furthermore, during the ball milling process, the material ratio of the ball milling beads to the first mixture is set to 18-22:1, and the rotation speed is 400-500 r / min. By setting a high ratio of ball milling beads, the particle size of the obtained second mixture is uniform. The specific material ratio of the ball milling beads to the first mixture and the rotation speed can be set according to actual conditions. For example, the material ratio of the ball milling beads to the first mixture can be set to 18:1, 20:1, or 22:1, and the rotation speed can be set to 400 r / min, 450 r / min, or 500 r / min.

[0066] S4. Subjecting the second mixture to high-temperature treatment to obtain a modified sodium ion battery positive electrode material.

[0067] In a specific embodiment, the treatment temperature is set to 650-750° C., and the treatment time is set to 5-7 hours.

[0068] Depend on Figure 1 It can be seen that the doping of tin elements is achieved through high-temperature solid-phase diffusion mechanism, in which Sn 4+ Ions are thermodynamically driven to replace transition metal lattice sites, forming a stable solid solution structure. This strategy can effectively suppress phase transition behavior during charge and discharge, significantly improving the intrinsic structural stability of the material. At the same time, the in-situ generated lithium fluoride (LiF) coating, through its excellent chemical inertness and ion selectivity, constructs a stable electrode-electrolyte interface, which can significantly inhibit the occurrence of interfacial side reactions such as electrolyte decomposition, thereby synergistically improving the electrochemical performance of the material.

[0069] Based on this, an embodiment of the present application also provides a P2 type sodium ion battery positive electrode material synergistically modified by tin doping and lithium fluoride coating, which is prepared by the aforementioned preparation method.

[0070] Based on this, the present application provides the application of the aforementioned P2 type sodium ion battery positive electrode material synergistically modified by tin doping and lithium fluoride coating in the preparation of sodium ion batteries.

[0071] The present application will be further described below in conjunction with more specific embodiments.

[0072] Example 1:

[0073] A method for preparing a positive electrode material for a sodium ion battery comprises the following steps:

[0074] S1. Obtain NFMO;

[0075] In this embodiment, NFMO is specifically Na 0.67 Fe 0.5 Mn 0.5 O2, obtaining NFMO includes the following steps:

[0076] S11. Dissolve NaNO3, Fe(NO3)3·9H2O, and Mn(CH3COO)2·4H2O in a molar ratio of 4:3:3 in deionized water to obtain a first solution.

[0077] S12. Continue stirring the first solution and add a citric acid solution to the first solution to obtain a second solution; wherein the molar ratio of total metal ions to citric acid in the second solution is maintained at 1:1.

[0078] S13, removing water from the second solution to obtain a gel-like primary product.

[0079] In this embodiment, S13 specifically includes the following steps:

[0080] S131. Heat the second solution at 60°C until no liquid remains on the surface to obtain a crude product.

[0081] S132, heat the crude product at 80°C for 12 h to obtain the primary product.

[0082] S14, finely grinding and calcining the primary product to obtain NFMO.

[0083] In this embodiment, calcining the primary product includes: pre-calcining the primary product at 450° C. in air for 4 hours, and then final calcining the primary product at 900° C. for 10 hours.

[0084] S2. Mixing the NFMO and the precursor to obtain a first mixture; wherein the mass ratio of the precursor to the NFMO is 0:100.

[0085] S3. Ball milling the first mixture to obtain a second mixture.

[0086] In this embodiment, the material ratio of ball milling beads to the first mixture during ball milling is 20:1, and the second mixture is ball milled at a speed of 450 r / min for 4 hours, wherein the forward ball milling is performed for 1 hour and the reverse ball milling is performed for 1 hour, and the cycle is repeated twice.

[0087] S4. Subjecting the second mixture to high-temperature treatment; wherein the treatment temperature is set to 700° C., and the treatment time is set to 6 hours, to obtain a modified sodium ion battery positive electrode material.

[0088] By the preparation method of this embodiment, a 0% NFMO sodium ion battery positive electrode material was prepared.

[0089] Example 2:

[0090] A method for preparing a positive electrode material for a sodium ion battery is the same as that in Example 1, except that in S2, the mass ratio of the precursor to NFMO is 1:100.

[0091] By the preparation method of this embodiment, a 1% NFMO sodium ion battery positive electrode material was prepared.

[0092] Example 3:

[0093] A method for preparing a positive electrode material for a sodium ion battery is the same as that in Example 1, except that in S2, the mass ratio of the precursor to NFMO is 3:100.

[0094] By the preparation method of this embodiment, a 3% NFMO sodium ion battery positive electrode material was prepared.

[0095] Example 4:

[0096] A method for preparing a positive electrode material for a sodium ion battery is the same as that in Example 1, except that in S2, the mass ratio of the precursor to NFMO is 5:100.

[0097] By the preparation method of this embodiment, a 5% NFMO sodium ion battery positive electrode material was prepared.

[0098] Comparative Example:

[0099] A method for preparing a positive electrode material for a sodium ion battery comprises the following steps:

[0100] S1. Dissolve NaNO3, Fe(NO3)3·9H2O and Mn(CH3COO)2·4H2O in a molar ratio of 4:3:3 in deionized water to obtain a first solution.

[0101] S2. Continue stirring the first solution and add citric acid solution to the first solution to obtain a second solution; wherein the molar ratio of total metal ions to citric acid in the second solution is maintained at 1:1.

[0102] S3. removing water from the second solution to obtain a gel-like primary product.

[0103] S3 specifically includes the following steps:

[0104] S31. Heat the second solution at 60°C until no liquid remains on the surface to obtain a crude product.

[0105] S32. Heat the crude product at 80°C for 12 h to obtain the primary product.

[0106] S4, finely grinding and calcining the primary product to obtain NFMO.

[0107] The NFMO sodium ion battery positive electrode material was prepared by the preparation method of this comparative example.

[0108] Sodium ion batteries were assembled using 0% NFMO, 1% NFMO, 3% NFMO, 5% NFMO and NFMO prepared in Examples 1 to 4 and the comparative example as positive electrode materials for sodium ion batteries, and the rate performance (discharge specific capacity), cycle performance and other properties of various sodium ion batteries were verified.

[0109] The main parameters of Examples 1 to 4 and the comparative example are shown in Table 1 below:

[0110] Table 1

[0111]

[0112] Depend on Figure 2 It can be seen that the samples prepared in Examples 1 to 4 all maintain the typical P2 type Na 0.67 Fe 0.5 Mn 0.5 O2 crystal structure (JCPDS standard card number 54-0894). X-ray diffraction (XRD) patterns show that the sample has obvious characteristic diffraction peaks at 2θ = 16.3° (002), 32.8° (004) and 38.5° (102), confirming the integrity of the P2 phase structure.

[0113] However, compared with the undoped sample, the diffraction peak intensity of the doped sample is significantly reduced (for example, the (002) peak intensity decreases by about 20%), and the diffraction peak appears slightly broadened. These changes are mainly due to:

[0114] 1) Sn 4+ Lattice distortion caused by doping;

[0115] 2) Formation of amorphous LiF coating on the surface.

[0116] It is particularly noteworthy that the (00l) crystal plane family diffraction peak shifts toward the low angle direction, indicating that the c-axis unit cell parameter has increased, which is the reason for the Na + The rapid transmission provides a more favorable structural channel.

[0117] Further references Figure 3 ,in Figure 3 a is the microscopic morphology of the comparative example, Figure 3 b is the microscopic morphology of Example 3.

[0118] Depend on Figure 3 It can be seen that the original NFMO material presents a typical hexagonal flake morphology, with an average particle size distribution in the range of 5-6μm, clear edges and a smooth surface. This regular morphological feature is consistent with its highly crystallized P2-type lamellar structure (space group P63 / mmc).

[0119] After ball milling modification, the morphology of NFMO particles changes significantly. The main manifestations are:

[0120] 1) The original hexagonal sheet structure breaks down to form an irregular polyhedron morphology;

[0121] 2) The average particle size is reduced to 4-5 μm, and the particle size distribution range is widened;

[0122] 3) The surface roughness of the particles increases significantly, and a large number of submicron surface defects appear.

[0123] These morphological changes are primarily attributed to particle breakage and surface reconstruction caused by mechanical forces during high-energy ball milling. Notably, while this morphological modification reduces the crystalline integrity of the material, it increases the number of active sites and provides a more adequate reaction interface for subsequent Sn doping and LiF coating.

[0124] Further references Figure 4 ,in Figure 4 c is the TEM image of the comparative example, Figure 4 d is the TEM image of Example 3, Figure 4 e is the EDS spectrum of the comparative example, Figure 4 f is the EDS spectrum of Example 3.

[0125] High-resolution transmission electron microscopy analysis revealed that the pristine NFMO material exhibited a highly ordered crystal structure, with clear lattice fringes with a spacing of 0.289 nm, corresponding to the (002) plane of the P63 / mmc space group. This feature closely matches the standard crystallographic parameters of P2-type layered oxides, confirming the material's excellent crystalline quality. Selected area electron diffraction (SAED) patterns exhibited typical hexagonal symmetry, further confirming the material's single-crystalline nature.

[0126] The modified samples show significant structural evolution compared to the original NFMO materials, which is manifested as follows:

[0127] 1) A uniform amorphous coating with a thickness of about 3-5 nm is formed on the surface, which is confirmed to be LiF phase by EDS composition analysis;

[0128] 2) (002) interplanar spacing expanded to 0.307nm, an increase of 6.2% compared with the original sample. This change is due to the Sn 4+ (ionic radius ) for Fe / Mn sites (Fe 3+ : Mn 4+ : ) substitution leads to lattice expansion;

[0129] 3) SAED patterns show that the modified sample retains the P63 / mmc space group signature, indicating that the modification process did not disrupt the material's fundamental crystal structure. EDS surface scanning analysis confirms the uniform distribution of Na, Fe, Mn, O, Sn, and F throughout the particles. The Sn signal intensity is consistent with the theoretical doping level, and F is primarily enriched in the particle surface, confirming the successful Sn doping and LiF coating.

[0130] Corresponding reference Figure 5 , X-ray photoelectron spectroscopy (XPS) analysis confirmed the presence of characteristic signals of Sn, Li and F on the surface of the modified material, and this result was highly consistent with the results of the EDS energy spectrum.

[0131] Reference Figure 6 ,XPS analysis shows that the F1s characteristic peak observed at 684.9eV is completely consistent with the bond energy characteristics of standard LiF.

[0132] It is worth noting that the peak position is significantly different from the F1s peak in SnF2. This chemical shift difference confirms that the surface of the material is not simply SnF2 residue, but a newly generated LiF phase through the solid-phase reaction of Li2CO3 and SnF2 during high-temperature calcination. It can be confirmed that the coating is pure phase LiF. This in-situ generated LiF coating has excellent chemical uniformity and interface bonding strength, providing stable interface protection for the electrode.

[0133] further, Figure 7 Please refer to Table 1 for the corresponding specific data. Figure 7 As shown in Table 1, under the voltage range of 1.5V to 4.2V, the current density was 0.5C, 1C, 2C, 3C and 5C respectively, and the charge and discharge cycle was carried out for 10 consecutive weeks. The discharge capacity of the sodium ion battery with 3% NFMO positive electrode material at 5C was 78.1mAh / g, which was significantly higher than that of the sodium ion battery assembled in other embodiments and the comparative example (1.1mAh / g). The improvement in the rate performance of the modified NFMO material is mainly due to the Sn 4+ Doping to expand the lattice spacing promotes Na + Diffusion, while the lithium fluoride coating stabilizes the interface and reduces the impedance, the two work together to make Na +The diffusion coefficient is increased by an order of magnitude, the interfacial charge transfer impedance is reduced, and the capacity retention rate at 5C rate is greatly improved compared with the unmodified sample, giving it better rate performance.

[0134] further, Figure 8 Please refer to Table 1 for the corresponding specific data. Figure 8 As shown in Table 1, under the voltage range of 1.5V to 4.2V and the current density of 1C, long charge and discharge cycles are carried out. The sodium ion batteries assembled with 0% NFMO, 1% NFMO, 3% NFMO and 5% NFMO positive electrode materials are cycled 200 times at a rate of 1C, and the capacity retention rates are 27.77%, 39.07%, 39.87% and 36.26%, respectively, which are significantly better than the 23.19% of the sodium ion battery assembled with unmodified NFMO positive electrode material.

[0135] Reference Figure 9 ,in Figure 9 a is the TEM image of the CV curve of the original NFMO (comparative example) at a scan rate of 0.1 mv / s. Figure 9 b is a TEM image of the CV curve of the modified sample (Example 3) at a scan rate of 0.1 mv / s.

[0136] Electrochemical cyclic voltammetry (CV) test results show that the modified sample (Example 3) exhibits a significantly enhanced redox peak current response within the 1.5-4.3V voltage window, directly corresponding to the increase in the material's specific capacity. Of particular note, after four cycles, the CV curves of the modified sample maintain a high degree of overlap, demonstrating excellent electrochemical reversibility, which is highly consistent with the capacity retention demonstrated in the long-cycle test.

[0137] Further, refer to Figure 10 The test results show that the Na + Apparent diffusion coefficient (DNa + ) is greatly improved compared with the original NFMO (comparative example). The sodium ion transfer coefficient calculated by the equation confirms the significant improvement of the interfacial reaction kinetics. The synergistic effects of doping and coating enable the modified material to maintain excellent Na + Diffusion dynamics characteristics.

[0138] The present application has been described in detail above. Specific examples have been used herein to illustrate the principles and implementation methods of the present application. The description of the above embodiments is intended only to facilitate understanding of the present application and its core concepts. It should be noted that, without departing from the principles of the present application, a number of improvements and modifications may be made to the present application by a person skilled in the art, and such improvements and modifications shall fall within the scope of protection of the claims of the present application.

Claims

1. A method for preparing a positive electrode material for a sodium ion battery, characterized in that: The following steps are involved: Get NFMO; Mixing NFMO with a precursor to obtain a first mixture; wherein the mass ratio of the precursor to the NFMO is 0 to 5:100, and the precursor includes lithium carbonate and tin fluoride; ball milling the first mixture to obtain a second mixture; The second mixture is subjected to high-temperature treatment to obtain a modified sodium ion battery positive electrode material.

2. The preparation method according to claim 1, characterized in that The mass ratio of the precursor to the NFMO is 1 to 5:

100.

3. The preparation method according to claim 1, characterized in that The molar mass ratio of the lithium carbonate to the tin fluoride is 1:1.5-2.

5.

4. The preparation method according to claim 1, characterized in that The time for ball milling the first mixture is set to 3 to 5 hours.

5. The preparation method according to claim 1, characterized in that When the second mixture is subjected to high-temperature treatment, the treatment temperature is set to 650-750° C., and the treatment time is set to 5-7 hours.

6. The preparation method according to claim 1, characterized in that The obtaining of NFMO comprises the following steps: Dissolving NaNO3, Fe(NO3)3·9H2O and Mn(CH3COO)2·4H2O in deionized water to obtain a first solution; continuously stirring the first solution and adding the citric acid solution to the first solution to obtain a second solution; removing water from the second solution to obtain a gel-like primary product; The primary product is finely ground and calcined to obtain NFMO.

7. The preparation method according to claim 6, characterized in that The molar ratio of total metal ions to citric acid in the second solution is maintained at 1:0.8 to 1:

2.

8. The preparation method according to claim 6, characterized in that The calcining of the primary product comprises the following steps: pre-calcining at 400-500° C. for 3-5 hours, and final calcining at 850-950° C. for 9-12 hours.

9. A sodium ion battery cathode material, characterized in that The preparation is carried out by the preparation method according to any one of claims 1 to 8.

10. Use of the sodium ion battery positive electrode material according to claim 9 in the preparation of a sodium ion battery positive electrode material.

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