Complex-phase high-entropy sodium ion battery positive electrode material with core-shell structure and preparation method and application of complex-phase high-entropy sodium ion battery positive electrode material

Abstract

The invention belongs to the technical field of sodium ion batteries, and discloses a complex-phase high-entropy sodium ion battery positive electrode material with a core-shell structure and a preparation method and application thereof.The preparation method comprises the steps that a TM source and a sodium source serve as raw materials, and a P2-phase sodium ion high-entropy positive electrode material is prepared; sodium is supplemented into the P2-phase sodium ion high-entropy positive electrode material, and the composite-phase high-entropy sodium ion battery positive electrode material with the core-shell structure is obtained through re-sintering, rapid cooling and vacuum drying. The positive electrode material has the P2 phase and the O3 phase with high crystallinity on the surface layer, has excellent cycle stability of the P2 phase and high specific capacity of the O3 phase, endows the corresponding sodium ion battery with high rate performance and long cycle stability, and the capacity retention ratio of the sodium ion battery corresponding to the positive electrode material reaches 90.7% after 2C cycles for 100 times, and the capacity retention ratio of the sodium ion battery corresponding to the positive electrode material reaches 85.6% after 5C cycles for 100 times.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery technology, specifically relating to a core-shell structured multiphase high-entropy sodium-ion battery cathode material, its preparation method, and its application. Background Technology

[0002] Sodium-ion batteries (SIBs) have become a promising next-generation energy storage technology after lithium-ion batteries due to their high energy density, excellent low-temperature performance, and low cost. As a key component of sodium-ion batteries, the cathode material is a crucial factor affecting their cycle performance. Cathode materials must possess high specific capacity, a suitable voltage window, high power density, excellent electronic / ionic conductivity, and good stability. Among commonly used sodium-ion battery cathode materials, transition metal layered oxide cathode materials have attracted much attention due to their high specific capacity and easy synthesis process; however, they suffer from air sensitivity, insufficient cycle stability, especially at high rates.

[0003] Depending on the sodium environment, transition metal layered oxide cathode materials are classified into P-type and O-type. Based on the oxygen layer stacking order, they can be further divided into P2-type, O2-type, P3-type, and O3-type. Among these, P2-type and O3-type have attracted widespread attention due to their higher thermodynamic stability. P2-type Na... x TMO2 (TM = two or three of Co, Mn, Ni, Fe, Cr, Cu, and V, 0.3 ≤ x ≤ 0.7) consists of two TMO2 layers, belonging to the P63 / mmc space group. It features wide migration channels, low migration barriers, fast migration kinetics, and high capacity. However, due to the strong Coulomb repulsion between adjacent sodium ions, an intermediate phase is easily formed. Excessive charge / discharge plateaus restrict sodium ion diffusion, and the P2 phase is prone to phase transitions, especially at high currents. These phase transitions lead to crystal structure distortion, reducing interlayer distance and affecting capacity retention. O3-type Na x TMO2 (x≈1) has a higher sodium content, providing more recyclable sodium. Previous research by the inventors (patent application CN18888744) shows that pure O3 phase layered cathode materials can significantly improve the initial discharge specific capacity of the battery. Other researchers have developed modification strategies such as surface coating and elemental doping. For example, phosphate core-shell coating can improve air stability, resulting in biphase cathode materials. However, regardless of whether pure phase layered materials are prepared or phosphate coating is applied, sodium-ion batteries still suffer from structural changes and capacity decay during long-term cycling, exhibiting poor rate performance and insufficient long-term cycle stability. Providing a sodium-ion battery cathode material with high stability and significantly improved rate performance is one effective way to solve these problems. Summary of the Invention

[0004] The technical problem this invention aims to solve is to address the shortcomings of the prior art by providing a core-shell structured multiphase high-entropy sodium-ion battery cathode material, its preparation method, and its applications. This addresses the issue that existing layered oxide cathodes in sodium-ion batteries cannot simultaneously achieve excellent rate performance and long-term cycle stability. The sodium-ion battery cathode material prepared using the method of this invention possesses a P2 phase and a highly crystalline O3 phase on the surface, combining the excellent cycle stability of the P2 phase with the high specific capacity of the O3 phase. This endows the corresponding sodium-ion battery with high rate performance and long-term cycle stability. The sodium-ion battery using the cathode material of this invention exhibits a capacity retention rate of up to 96.7% after 100 cycles at 0.1C, 92.1% after 100 cycles at 1C, 90.7% after 100 cycles at 2C, and 85.6% after 100 cycles at 5C, demonstrating high electrochemical performance and cycle stability even at high rates (2C~5C).

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0006] In a first aspect, a method for preparing a core-shell structured multiphase high-entropy sodium-ion battery cathode material is provided, comprising:

[0007] P2 phase sodium ion high-entropy cathode material was prepared using TM source and sodium source as raw materials;

[0008] Sodium was added to the P2 phase sodium-ion high-entropy cathode material, and after reheating, rapid cooling and vacuum drying, a core-shell structured multiphase high-entropy sodium-ion battery cathode material was obtained.

[0009] On the other hand, a core-shell structured high-entropy sodium-ion battery cathode material is provided using the above preparation method.

[0010] On the other hand, this paper provides an application of the aforementioned core-shell structured multiphase high-entropy sodium-ion battery cathode material in sodium-ion batteries.

[0011] Compared with the prior art, the present invention has the following advantages:

[0012] 1. This invention provides a method for preparing a core-shell structured multiphase high-entropy sodium-ion battery cathode material. By performing sodium replenishment and re-firing, rapid cooling and vacuum drying on the P2 phase, a sodium-rich O3 phase shell is generated on the surface of the sodium-deficient P2 phase particles. The resulting cathode material combines the excellent cycle stability of the P2 phase with the high specific capacity of the O3 phase, giving the corresponding sodium-ion battery high rate performance and long cycle stability.

[0013] 2. The preparation method of the core-shell structured multiphase high-entropy sodium-ion battery cathode material of the present invention includes rapid cooling and vacuum drying of the material after sodium replenishment and recalcination, which induces lattice distortion and element redistribution, promotes the kinetic segregation of specific protective elements (such as Ti) in the near-surface region, freezes non-equilibrium micro-defects, and reduces structural stress. In addition, vacuum drying can also remove surface water vapor condensation caused by rapid cooling, and obtain a multiphase with high crystallinity and stable structure. This multiphase material solves the problem that layered oxide cathodes cannot simultaneously accommodate the P2 phase and the highly crystallinity O3 phase, and endows the cathode material with higher structural stability, high specific capacity and excellent cycle performance.

[0014] 3. The method for preparing the core-shell structured multiphase high-entropy sodium-ion battery cathode material of the present invention is simple and efficient, and suitable for industrial production.

[0015] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0016] Figure 1 A schematic diagram showing the XRD characterization test results of the cathode materials obtained in each embodiment and comparative example within a wide 2θ range;

[0017] Figure 2 This is a schematic diagram showing the XRD characterization test results of the cathode materials obtained in the small 2θ range of each embodiment and comparative example. Detailed Implementation

[0018] The technical solution will now be clearly and completely described with reference to the embodiments of this application. Obviously, the described embodiments are only a part of the embodiments of this application, not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0019] In the following description, the term "and / or" is used to describe the relationship between related objects, indicating that there can be three relationships. For example, A and / or B can mean: A exists alone, B exists alone, and A and B exist simultaneously. A and B can be singular or plural.

[0020] In the following description, the terms “including,” “containing,” “having,” and “containing” are open-ended terms, meaning that they include but are not limited to.

[0021] Those skilled in the art should understand that, in the following description of the embodiments of this application, the sequence of numbers does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0022] Those skilled in the art will understand that the numerical ranges in the embodiments of this application should be understood to specifically disclose each intermediate value between the upper and lower limits of the range. Each smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this application. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0023] Unless otherwise stated, the technical / scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. While this application describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this application. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0024] The reaction principle upon which this invention is based is as follows: the prepared P2 phase sodium ion high-entropy cathode material is subjected to sodium replenishment and re-firing, rapid cooling and vacuum drying to obtain an O3 phase with high surface crystallinity, thus obtaining a core-shell structured multiphase high-entropy sodium ion battery cathode material formed by the composite of the P2 phase and the O3 phase.

[0025] In a first aspect, a method for preparing a core-shell structured multiphase high-entropy sodium-ion battery cathode material is provided, comprising:

[0026] P2 phase sodium ion high-entropy cathode material was prepared using TM source and sodium source as raw materials;

[0027] Sodium was added to the P2 phase sodium-ion high-entropy cathode material, and after reheating, rapid cooling and vacuum drying, a core-shell structured multiphase high-entropy sodium-ion battery cathode material was obtained.

[0028] This invention obtains a core-shell structured, multiphase high-entropy sodium-ion battery cathode material by adding sodium to the P2 phase, followed by recalcination, rapid cooling, and vacuum drying. This cathode material is composed of a P2 phase and a highly crystalline O3 phase on the surface. The surface layer of this cathode material is the O3 phase, with enriched surface protective elements and a uniformly distributed TM layer. It exhibits high crystallinity, no residual moisture on the surface, and corresponds to high rate performance and long cycle stability in sodium-ion batteries.

[0029] In some embodiments, the TM source is an oxide, hydroxide, or salt of TM, and the TM includes two or more of Co, Mn, Ni, Fe, Cr, Ti, Cu, and V. The sodium source is one or more of sodium acetate, sodium carbonate, sodium bicarbonate, sodium hydroxide, sodium chloride, and sodium sulfate. The amounts of the TM source and the sodium source are based on the stoichiometric ratio of each element in the high-entropy layered cathode material of the sodium-ion battery. In some preferred embodiments, the TM source is an oxide of TM, and the TM includes Ni, Fe, Mn, Cu, and Ti. The sodium source is sodium carbonate and / or sodium hydroxide. The stoichiometric ratio of Ni, Fe, Mn, Cu, and Ti in the P2 phase sodium-ion high-entropy cathode material is 0.25:0.25:0.25:0.125:0.125.

[0030] In some embodiments, the preparation of P2-phase sodium-ion high-entropy cathode material using TM source and sodium source as raw materials specifically includes: ball milling and mixing TM source and sodium source to obtain a mixture, and calcining the mixture to obtain P2-phase sodium-ion high-entropy cathode material; the ball milling rate is 300~600 rpm, and the ball milling time is 4~12 h; in some preferred embodiments, the ball milling rate is 400 rpm, and the ball milling time is 6 h; in some embodiments, the calcination is programmed temperature calcination, with a heating rate of 5℃ / min, a calcination temperature of 800~1000℃, and a calcination time of 12~24 h; in some preferred embodiments, the calcination temperature is 900℃, and the calcination time is 20 h.

[0031] In some embodiments, sodium is added to the P2 phase sodium ion high-entropy cathode material by adding a sodium source to the P2 phase sodium ion high-entropy cathode material; the mass of the added sodium source is 1% to 4% of the mass of the sodium source used to prepare the P2 phase sodium ion high-entropy cathode material.

[0032] In some embodiments, the core-shell structured complex high-entropy sodium-ion battery cathode material is a complex high-entropy sodium-ion battery cathode material formed by the composite of P2 phase and O3 phase, wherein the mass ratio of O3 phase in the cathode material is 10% to 20%.

[0033] In some embodiments, the reheating temperature is 650~700°C. In some preferred embodiments, the reheating is performed by heating to 700°C at a rate of 5°C / min and holding at 700°C for 5 hours.

[0034] Compared to the P2 phase, the O3 phase layered material has a higher sodium content and a more complex oxygen atom stacking structure. The common sintering temperature of the O3 phase is ≥800℃. During the research process, the inventors discovered that in the process of preparing a core-shell structured multiphase high-entropy sodium-ion battery cathode material, the re-firing temperature is lowered to 650~750℃ after sodium supplementation, which can obtain a multiphase material with higher O3 crystallinity. A high re-firing temperature is actually not conducive to obtaining a highly crystalline O3 shell.

[0035] In some embodiments, the rapid cooling is performed by a rapid cooling medium, which is one or more of liquid nitrogen, liquid helium, liquid argon, cryogenic water, and liquid carbon dioxide; the rapid cooling is from 400~500°C to room temperature; in some preferred embodiments, the rapid cooling medium is liquid nitrogen.

[0036] The preparation method of the present invention includes adding a sodium source to the P2 phase for re-firing, and then rapidly cooling the re-firing phase using a rapid cooling medium to promote the enrichment of protective elements near the surface of the grains and induce the formation of a sodium-rich O3 phase shell on the surface of the sodium-deficient P2 phase.

[0037] In some embodiments, the vacuum drying temperature is 80~200℃ and the vacuum drying time is 8~12h; in some preferred embodiments, the vacuum degree is -0.09MPa, the vacuum drying temperature is 120℃, and the vacuum drying time is 12h.

[0038] The preparation method of this invention also includes immediate vacuum drying of the material after rapid cooling. During the research process, the inventors discovered that rapid cooling with liquid nitrogen causes water vapor to condense on the surface of the material, affecting the formation of the O3 phase and the stability of the structure. By immediately vacuum drying the material after rapid cooling, the surface moisture can be effectively removed, promoting the enrichment of Ti, the protective element near the surface of the grains, while avoiding the dissolution of other TM phases. With the support of these uniformly distributed TM phases, the sodium-deficient P2 phase surface layer forms a sodium-rich O3 phase shell, obtaining a composite high-entropy sodium-ion battery cathode material with a highly stable O3 and P2 phase structure. This composite high-entropy sodium-ion battery cathode material can effectively avoid side reactions between the surface layer and the electrolyte, giving sodium-ion batteries higher electrochemical performance in high-rate and long-cycle tests.

[0039] On the other hand, a core-shell structured high-entropy sodium-ion battery cathode material is provided using the above preparation method.

[0040] On the other hand, this paper provides an application of the aforementioned core-shell structured multiphase high-entropy sodium-ion battery cathode material in sodium-ion batteries.

[0041] Prior to the application for this invention, a series of experiments were conducted. Some of the experimental results are listed below to provide a more detailed description of the invention. The following is a detailed description in conjunction with the embodiments.

[0042] Example 1

[0043] This embodiment provides a method for preparing a core-shell structured multiphase high-entropy sodium-ion battery cathode material, including:

[0044] Step 1: Mix 7.24g (2% excess) of Na2CO3, 3.73g of NiO, 3.99g of Fe2O3, 4.35g of MnO2, 1.99g of CuO, and 2.00g of TiO2 in a ball mill jar and ball mill at 400rpm for 6 hours to obtain a mixture. Use a sodium source in 2% excess by mass to reduce the impact of sodium source loss on the product during the synthesis process.

[0045] Step 2: Transfer the mixture to a muffle furnace and heat it to 900°C at a rate of 5°C / min. Calcinate the mixture at 900°C for 20 hours to obtain P2-Na. 0.67 Ni 0.25 Fe 0.25 Mn 0.25 Cu 0.125 Ti 0.125 O2 high-entropy materials;

[0046] Step 3: P2-Na 0.67 Ni 0.25 Fe 0.25 Mn 0.25 Cu 0.125 Ti 0.125 O2 high-entropy material was mixed with 0.136 g (2% excess) of NaOH and placed in a muffle furnace. The temperature was increased to 700 °C at a rate of 5 °C / min, and then calcined at 700 °C for 5 h. Heating was then stopped, and the mixture was allowed to cool naturally to 500 °C. After being removed from the muffle furnace, the material was rapidly cooled to 25 °C with liquid nitrogen for less than 1 min. Following rapid cooling, the material was dried in a vacuum drying oven at 120 °C and a vacuum degree of -0.09 MPa for 12 h to obtain a core-shell high-entropy cathode material, wherein the shell layer is O3-NaNi. 0.25 Fe 0.25 Mn 0.25 Cu 0.125 Ti 0.125 The O2 content is 10% by mass; the amount of NaOH added is calculated according to the following formula: Of which 10% is the mass percentage of shell O3, m P2 For P2-Na in step three 0.67 Ni 0.25 Fe 0.25 Mn 0.25 Cu 0.125 Ti 0.125 The mass of O2 (g, M) p2P2-Na 0.67 Ni 0.25 Fe 0.25 Mn 0.25 Cu 0.125 Ti 0.125 The molecular weight of O2, M NaOH is the molecular weight of NaOH.

[0047] Example 2

[0048] This embodiment provides a method for preparing a core-shell structured multiphase high-entropy sodium-ion battery cathode material, which is the same as in Example 1, except that the mass of NaOH in step three is 0.204 g (2% excess), and the resulting high-entropy cathode material has an O3-NaNi shell. 0.25 Fe 0.25 Mn 0.25 Cu 0.125 Ti 0.125 O2 accounts for 15% of the total mass.

[0049] Example 3

[0050] This embodiment provides a method for preparing a core-shell structured multiphase high-entropy sodium-ion battery cathode material, which is the same as in Example 1, except that the mass of NaOH in step three is 0.272 g (2% excess), and the resulting high-entropy cathode material has an O3-NaNi shell. 0.25 Fe 0.25 Mn 0.25 Cu 0.125 Ti 0.125 O2 accounts for 20% of the total mass.

[0051] Comparative Example 1

[0052] This comparative example provides a method for preparing a sodium-ion battery cathode material, including:

[0053] Step 1: Mix 7.24g (2% excess) of Na2CO3, 3.73g of NiO, 3.99g of Fe2O3, 4.35g of MnO2, 1.99g of CuO, and 2.00g of TiO2 in a ball mill jar and ball mill at 400rpm for 6 hours to obtain a mixture.

[0054] Step 2: Transfer the mixture to a muffle furnace and heat it to 900°C at a rate of 5°C / min. Calcinate the mixture at 900°C for 20 hours to obtain the cathode material (P2-Na). 0.67 Ni 0.25 Fe 0.25 Mn 0.25 Cu 0.125 Ti 0.125 O2).

[0055] Comparative Example 2

[0056] This comparative example provides a method for preparing a sodium-ion battery cathode material, including:

[0057] Step 1: Mix 7.24g (2% excess) of Na2CO3, 3.73g of NiO, 3.99g of Fe2O3, 4.35g of MnO2, 1.99g of CuO, and 2.00g of TiO2 in a ball mill jar and ball mill at 400rpm for 6 hours to obtain a mixture.

[0058] Step 2: Transfer the mixture to a muffle furnace and heat it to 900°C at a rate of 5°C / min. Calcinate the mixture at 900°C for 20 hours to obtain P2-Na. 0.67 Ni 0.25 Fe 0.25 Mn 0.25 Cu 0.125 Ti 0.125 O2 high-entropy materials;

[0059] Step 3: Add 0.136g (2% excess) of NaOH and mix. Place the mixture in a muffle furnace and heat it to 700℃ at a rate of 5℃ / min. After reheating at 700℃ for 5 hours, cool it down to 500℃. Remove it from the muffle furnace and rapidly cool it to 25℃ with liquid nitrogen within 1 minute. After rapid cooling, immediately perform low-temperature tempering, i.e., heat it to 300℃ at a rate of 2℃ / min and hold it at 300℃ for 4 hours to obtain the cathode material.

[0060] Performance Evaluation

[0061] XRD characterization was performed on the cathode materials of each embodiment and comparative example, and the results showed that... Figure 1 and Figure 2In the XRD characterization results of Example 1, the (002) peak at 15.9° shifted to the right, and the characteristic peak (104) of the O3 phase appeared at around 41.9°, indicating that the cathode material of Example 1 was a composite phase of O3 and P2. In Example 2, the (002) peak at 15.9° shifted to the right, and the characteristic peak (104) of the O3 phase at around 41.9° became stronger, indicating that the cathode material of Example 2 was a composite phase of O3 and P2. In Example 3, the (002) peak at 15.9° shifted to the right, and the characteristic peak (104) of the O3 phase at around 41.9° became stronger, indicating that the cathode material of Example 3 was a composite phase of O3 and P2. The XRD characterization results of the cathode material of Comparative Example 1 showed that there was no characteristic peak of the O3 phase, and the obtained material was a pure P2 phase material. The XRD spectrum of Comparative Example 2 shows that the peak intensity of the characteristic peak (104) of the O3 phase at 41.9° is significantly weaker. It can be seen that compared with vacuum drying, tempering treatment will affect the formation of the O3 phase. The possible reason is that tempering treatment will affect the crystallization of the surface O3 phase structure. Figure 1 XRD characterization of Example 1 showed that O3 phase characteristic peaks appeared in the main P2 phase material. Combined with the preparation process of the P2 phase, it can be known that these are surface O3 phase diffraction peaks. The method of the present invention successfully synthesized a core-shell structure with an O3 phase on the surface.

[0062] Electrochemical tests were conducted on the positive electrode materials of each embodiment and comparative example. The method for preparing the coin cell included: mixing the positive electrode material with acetylene black and binder in an 8:1:1 ratio, adding N-methylpyrrolidone and mixing thoroughly to form a slurry, then uniformly coating the slurry onto aluminum foil with a 100 μm scraper, drying and cutting it into circular pieces with a diameter of 12 mm to obtain the sodium-ion battery positive electrode. The positive electrode was used as the electrode sheet, and the sodium sheet was used as the counter electrode. The electrolyte was obtained by dissolving 1M sodium perchlorate in a solvent with a mass ratio of propylene carbonate and ethylene carbonate of 1:1, and adding 5% fluoroethylene carbonate. Glass fiber was used as the separator to assemble the sodium-ion coin cell, wherein the amount of electrolyte was about 120 μL / cell, and it was evenly distributed on both sides of the separator to obtain the coin cell. The obtained coin cells were electrochemically tested at room temperature, and the tested voltage range was 2.0~4.0V. The electrochemical performance is shown in Tables 1~3.

[0063] Table 1. Electrochemical performance test results (mAh / g) of Examples 1-3 and Comparative Examples 1-2

[0064]

[0065] Table 2. Rate performance test results (mAh / g) of Examples 1-3 and Comparative Examples 1-2

[0066]

[0067] Table 3. High-rate cycling performance test results of Examples 1-3 and Comparative Examples 1-2

[0068]

[0069] As shown in Table 1, compared with Comparative Example 1, each embodiment exhibits significantly improved low-rate (0.1C~1C) performance, indicating that the multiphase high-entropy sodium-ion battery cathode material of the present invention possesses relatively higher electrochemical performance. Each embodiment and Comparative Example 2 exhibit essentially equivalent low-rate (0.1C~1C) performance. In the low-rate long-cycle performance test of each embodiment, the discharge specific capacity and capacity retention rate after 100 cycles are significantly higher than those of the comparative examples, indicating that the cathode material prepared using the method of the present invention has significantly improved low-rate electrochemical stability.

[0070] Table 2 shows the rate performance test results of each embodiment and comparative example. It can be seen that each embodiment has a significantly improved low-rate (0.1C~1C) discharge specific capacity compared with Comparative Example 1, and the low-rate (0.1C~1C) discharge specific capacity of each embodiment is not much different from that of Comparative Example 2. At high rates (2C~5C), the discharge specific capacity of each embodiment is significantly higher than that of each comparative example, indicating that the cathode material prepared by the method of the present invention has significantly improved high-rate electrochemical performance.

[0071] Table 3 shows the comparison results of the cycling performance of each embodiment and comparative example at various rates. It can be seen that at low rates (0.1C~1C), the long-cycle capacity retention rates of each embodiment and the comparative example are basically equivalent. At high rates (2C~5C), the long-cycle capacity retention rates of each embodiment are significantly higher than those of the comparative example. This indicates that the cathode material prepared using the method of this invention has significantly improved high-rate cycling stability. Combined with XRD characterization results, it can be seen that the cathode material prepared using the method of this invention combines the excellent cycling stability of the P2 phase with the high specific capacity of the O3 phase. Compared to rapid cooling + low-temperature tempering, the rapid cooling + vacuum drying method used in this invention is more advantageous in obtaining an O3 phase with high surface crystallinity and can effectively remove the influence of surface moisture on electrochemical performance.

Claims

1. A method for preparing a core-shell structured multiphase high-entropy sodium-ion battery cathode material, characterized in that, The application relates to a preparation method of a core-shell structure composite high-entropy sodium ion battery cathode material. The P2 phase sodium ion high-entropy cathode material is prepared from a TM source and a sodium source. The TM source is an oxide, a hydroxide or a salt of TM, the TM includes two or more of Co, Mn, Ni, Fe, Cr, Ti, Cu and V, and the sodium source is one or more of sodium acetate, sodium carbonate, sodium bicarbonate, sodium hydroxide, sodium chloride and sodium sulfate.

2. The method for preparing the core-shell structured complex-phase high-entropy sodium-ion battery cathode material according to claim 1, characterized in that, The P2 phase sodium ion high-entropy cathode material is prepared from a TM source and a sodium source.

3. The method of claim 1, wherein the method further comprises: The ball milling speed is 300-600 rpm, and the ball milling time is 4-12 h; the calcination is programmed temperature calcination, the temperature rising rate is 5 DEG C / min, the calcination temperature is 800-1000 DEG C, and the calcination time is 12-24 h.

4. The method of claim 3, wherein the method further comprises: The sodium source is added to the P2 phase sodium ion high-entropy cathode material; the temperature of the re-calcination is 650-700 DEG C.

5. The method for preparing the core-shell structured multiphase high-entropy sodium-ion battery cathode material according to claim 1, characterized in that, The mass of the added sodium source is 1%-4% of the mass of the sodium source used for preparing the P2 phase sodium ion high-entropy cathode material.

6. The method of claim 5, wherein the method further comprises: The quenching medium is one or more of liquid nitrogen, liquid helium, liquid argon, low-temperature water and liquid carbon dioxide; the quenching is from 400-500 DEG C to room temperature; the temperature of the vacuum drying is 80-200 DEG C, and the vacuum drying time is 8-12 h.

7. The method of claim 1, wherein the method further comprises: The core-shell structure composite high-entropy sodium ion battery cathode material is a composite high-entropy sodium ion battery cathode material formed by P2 phase and O3 phase, and the mass ratio of the O3 phase in the cathode material is 10%-20%.

8. The method of claim 1, wherein the method further comprises:

9. A core-shell structure composite high-entropy sodium ion battery cathode material prepared by the preparation method of the core-shell structure composite high-entropy sodium ion battery cathode material in claim 1.

10. Application of the core-shell structure composite high-entropy sodium ion battery cathode material in claim 9 to a sodium ion battery. ​

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