Preparation method of a dual-phase proportion-adjustable high-entropy positive electrode material sodium ion battery

Abstract

The application discloses a preparation method of a high-entropy positive electrode material sodium ion battery with a two-phase ratio that can be adjusted, and steps of the method comprise the following steps: S1, mixing a sodium source, an iron source, a cobalt source, a nickel source, a manganese source and a titanium source according to the element composition of the positive electrode material of the sodium ion battery, replacing the titanium element with copper in an equal-molar manner, and obtaining a mixed powder sample after sufficient ball milling; S2, mixing according to the element composition of the adjusted positive electrode material; S3, tabletting the raw material mixture sample and high-temperature sintering, and cooling to room temperature; S4, mixing the positive electrode material with a conductive additive and polyvinylidene fluoride, and adding N-methylpyrrolidone solvent; and S5, assembling the prepared positive electrode sheet and a metal sodium sheet negative electrode into a sodium ion battery. The application can realize the adjustment of the P2 / O3 phase ratio of the positive electrode material of the sodium ion battery by only replacing the titanium element with the copper element, improves the specific capacity of the positive electrode material, has high specific capacity, and is easy to realize large-scale production.

Description

TECHNICAL FIELD

[0001] The application relates to a preparation method of a sodium ion battery, in particular to a preparation method of a high-entropy positive electrode material sodium ion battery with adjustable phase ratio, and belongs to the battery preparation field. BACKGROUND

[0002] In recent years, there has been growing interest in the various applications of sodium ion batteries (SIBs), especially large-scale energy storage. This development is due to the exponential growth in global energy and societal demand for material sustainability. Compared with widely used lithium ion batteries (LIBs), sodium ion batteries are a viable alternative due to their lower cost and the use of abundant resources, sodium. The research on anodes has mainly focused on layered oxides NaxTMO2 (TM = transition metal) with various structures, which have high theoretical specific capacity, high operating potential, and good Na+ transport performance. Developing high-capacity, high-potential positive electrode materials is crucial for their practical application. In the past decade, various positive electrode materials such as oxides, polyanion compounds, and Prussian blue analogues have been proposed. Among them, layered oxide materials have been widely studied due to their excellent electrochemical performance. Due to the different stacking modes of sodium ions, sodium-based layered materials can generally be classified as P-type and O-type. Among them, P-type refers to sodium ions occupying trigonal prism positions; O-type refers to sodium ions occupying octahedral positions.

[0003] High-entropy oxides are generally composed of 5 or more elements in equal atomic ratios or close to equal atomic ratios. Each element forms a joint lattice by sharing the same atomic sites, and is arranged in disorder in the crystal. This disordered distribution and the interaction between different metal ions greatly increases the mixing entropy, effectively inhibiting the formation of intermetallic compounds or complex phases, thus tending to generate single-phase solid solution structures. Based on the high-entropy effect in thermodynamics, the sluggish diffusion effect in dynamics, the lattice distortion effect in structure, and the "cocktail" effect in performance similar to high-entropy alloys, high-entropy oxides exhibit some characteristics far superior to traditional oxides, such as extremely high structural stability, abnormal dielectric constant, and ultra-high lithium ion and sodium ion conductivity. These characteristics have aroused the research interest of energy storage researchers in high-entropy oxides, especially high-entropy oxides with a two-phase structure.

[0004] However, in the prior art, the phase ratio of the prepared two-phase structure material is single and cannot be adjusted, and contains Li + , Sb 5+ and other metal elements, which are expensive and some elements are toxic, hindering large-scale production. SUMMARY

[0005] To address the problems existing in the prior art, the present invention aims to provide a method for preparing a sodium-ion battery with a high-entropy cathode material whose phase ratio can be adjusted in a two-phase manner, thereby solving the problems of existing two-phase electrode materials having a single, uncontrollable phase ratio, high cost, and environmental hazards.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A method for preparing a sodium-ion battery with a high-entropy cathode material and adjustable dual-phase ratio includes the following steps:

[0008] S1: Sodium, iron, cobalt, nickel, manganese, and titanium sources are mixed according to the elemental composition of sodium-ion battery cathode materials. Then, according to the atomic ratio control requirements, the titanium portion is equimolarly replaced with copper, where the molar ratio of copper to titanium is 0-10 (excluding values ​​of 0 and 10). After thorough ball milling, a mixed powder sample is obtained with a particle size of 10-200 nm. The elemental composition of the sodium-ion battery cathode material is Na. 0.65-0.75 (Fe 0.2 Co 0.2 Ni 0.2 Cu x Mn y Ti 0.44-x-y O2, where 0.15≤y≤0.3, 0<x≤0.15;

[0009] S2: Mix the raw materials according to the elemental composition of the regulated cathode material to obtain a raw material mixture;

[0010] S3: The raw material mixture sample is pressed into tablets under 10-25 MPa conditions and then sintered at high temperature of 600-1200℃ for 10-24h in an atmosphere of air or oxygen, wherein the heating rate from room temperature to sintering temperature is 3-10℃ / min. Then it is cooled to room temperature to obtain sodium-ion battery cathode material with the ratio of P2 phase and O3 phase adjusted.

[0011] S4: The positive electrode material, conductive additive, and polyvinylidene fluoride are mixed in a mass ratio of 7:2:1, and an appropriate amount of N-methylpyrrolidone solvent is added. The positive electrode sheet is prepared through processes such as slurry mixing, coating, and drying, with an active material loading of 2-3.5 mg / cm³. -2 ;

[0012] S5: The prepared positive electrode and the sodium metal negative electrode are assembled into a sodium-ion battery. The electrolyte consists of 1 mol / L NaPFO6, a mixed solvent of propylene carbonate / ethyl methyl carbonate in a volume ratio of 1:1, and 4% fluoroethylene carbonate. The separator is a porous glass carbon fiber membrane. The coin cell is assembled in a glove box filled with argon gas and the water oxygen value is below 0.1 ppm.

[0013] Preferably, the method of mixing raw materials in step S2 includes any one or a combination of at least two of ball milling, co-precipitation, and sol-gel mixing.

[0014] Preferably, the sodium source includes any one or a combination of at least two of sodium carbonate, sodium citrate, sodium acetate, and sodium nitrate.

[0015] Preferably, the iron source includes any one or a combination of at least two of ferric oxide, ferric oxide, ferric nitrate, and ferric acetate.

[0016] Preferably, the cobalt source includes any one or a combination of at least two of cobalt trioxide, cobalt tetroxide, cobalt citrate, and cobalt nitrate.

[0017] Preferably, the nickel source includes any one or a combination of at least two of nickel oxide, nickel hydroxide, nickel acetate, and nickel nitrate.

[0018] Preferably, the copper source includes any one or a combination of at least two of copper oxide, copper citrate, copper acetate, and copper nitrate.

[0019] Preferably, the manganese source includes any one or a combination of at least two of manganese trioxide, manganese oxide, manganese acetate, manganese nitrate, and manganese hydroxide.

[0020] Preferably, the titanium source is titanium dioxide.

[0021] The beneficial effects of this invention are as follows: the ratio of the P2 / O3 phase in the sodium-ion battery cathode material can be adjusted simply by controlling the elements, and by combining the advantages of multiple elements in the material, the specific capacity of the high-entropy cathode material is improved to a certain extent. Moreover, the high specific capacity makes it easy to achieve large-scale production. Attached Figure Description

[0022] Figure 1 The sodium-ion cathode material Na obtained in Example 1 of this invention 0.70 (Fe 0.2 Co 0.2 Ni 0.2 Cu 0.03 Mn 0.2 Ti 0.21 XRD patterns of high-entropy oxides of O2;

[0023] Figure 2 The sodium-ion cathode material Na obtained in Example 1 of this invention 0.70 (Fe 0.2 Co 0.2 Ni 0.2 Cu 0.03 Mn 0.2 Ti 0.21 SEM image of high-entropy oxides of O2;

[0024] Figure 3 The sodium-ion cathode material Na obtained in Example 1 of this invention 0.70 (Fe 0.2 Co 0.2 Ni 0.2 Cu 0.03 Mn 0.2 Ti 0.21 Charge-discharge rate performance curves of sodium-ion batteries assembled with O2 high-entropy oxides.

[0025] Figure 4 , Figure 5 The sodium-ion cathode material Na obtained in Example 1 of this invention 0.70 (Fe 0.2 Co 0.2 Ni 0.2 Cu 0.03 Mn 0.2 Ti 0. 21 The charge-discharge cycle performance curves of sodium-ion batteries assembled with O2 high-entropy oxides under current density conditions of 0.5C and 1C. Detailed Implementation

[0026] The present invention will now be described in further detail with reference to the accompanying drawings. The technical solution of the present invention will be further explained and illustrated below with reference to specific embodiments. However, it should be noted that the specific embodiments are merely a specific implementation and explanation of the essence of the technical solution of the present invention, and should not be construed as a limitation on the scope of protection of the present invention.

[0027] Example 1

[0028] (1) Sodium carbonate, ferric oxide, cobalt oxide, nickel oxide, copper oxide, manganese dioxide, and titanium dioxide are arranged according to the elemental composition of sodium-ion battery cathode materials. 0.70 (Fe 0.20 Co 0.20 Ni 0.20 Cu 0.03 Mn 0.20 Ti 0.21 The O2 was mixed in a certain proportion and ball-milled thoroughly to obtain a mixed powder sample with a particle size of 10-100 nm (average particle size of 50 nm);

[0029] The ball milling method is exemplified as follows: sodium, iron, cobalt, nickel, copper, manganese, and titanium sources are placed in an agate ball milling jar in corresponding proportions. After loading the jar, a certain amount of auxiliary agent is added, followed by ball milling. The auxiliary agent is one or a mixture of ethanol and methanol. Ball milling is performed (e.g., at a speed of 450–600 rpm for 6–12 hours). After ball milling, the mixture is dried at a temperature of 40–90°C for 6–24 hours to obtain a mixed powder.

[0030] An exemplary embodiment of the sol-gel method is as follows: Sodium, iron, cobalt, nickel, copper, manganese, and titanium sources are dissolved in deionized water in corresponding proportions. A certain amount of citric acid solution (the molar ratio of metal ions to citric acid can be 1:1 to 3.5) is added dropwise to the above solution. The solution is heated in a water bath (e.g., 65 to 90°C) until it evaporates to dryness and forms a gel. The gel is then heated (e.g., at 110 to 130°C for more than 20 hours) to obtain a mixed powder.

[0031] The coprecipitation method is exemplified as follows: iron, cobalt, nickel, copper, and manganese sources are dissolved in deionized water, ammonia and sodium hydroxide are added, the pH is adjusted to alkaline (e.g., 9.5-11), and then aged (e.g., aged at 40-60℃ for more than 24 hours) to obtain hydroxide precursors. The precursor powder is then manually ground with sodium and titanium sources in a mortar in a certain proportion to obtain mixed powder.

[0032] (2) The mixed powder sample obtained in step (1) is pressed into a disc with a diameter of 14 cm using a tablet press at 17 MPa. The disc is then sintered in air at a heating rate of 5 °C / min to 700 °C for 10 h, and then sintered at a heating rate of 5 °C / min to 950 °C for 15 h. After being cooled to room temperature in the furnace, sodium-ion battery cathode material is obtained.

[0033] like Figure 1 As shown, the sodium-ion battery cathode material Na obtained in this embodiment 0.70 (Fe 0.20 Co 0.20 Ni 0.20 Cu 0.03 Mn 0.20 Ti 0.21 The XRD diffraction pattern of the O2 high-entropy layered oxide conforms to the PDF card of the P2 and O3 phase structures. That is, by adjusting the ratio of copper to titanium to 1:7, the Na content in the obtained material can be determined. 0.70 (Fe 0.20 Co 0.20 Ni 0.20 Cu 0.03 Mn 0.20 Ti 0.21O2 is a mixture of P2 and O3 phases, with a ratio of 0.24:0.76 between the P2 and O3 phases.

[0034] like Figure 2 As shown, the sodium-ion battery cathode material Na obtained in this embodiment 0.70 (Fe 0.20 Co 0.20 Ni 0.20 Cu 0.03 Mn 0.20 Ti 0.21 The high-entropy oxides of O2 have uniform morphology and a particle size of 0.5–5 μm.

[0035] Battery assembly:

[0036] (1) Preparation of positive electrode:

[0037] The positive electrode material, conductive additive (SuperP), and binder (polyvinylidene fluoride) were mixed at a mass ratio of 7:2:1, and an appropriate amount of solvent (N-methylpyrrolidone) was added. The positive electrode sheet (with an active material loading of 2–3.5 mg / cm³) was prepared through processes including slurry mixing, coating, and drying. -2 );

[0038] (2) Assembling sodium-ion batteries:

[0039] The prepared positive electrode and the sodium metal negative electrode were assembled into a sodium-ion battery; the electrolyte consisted of a mixed solvent of 1 mol / L NaPFO6, propylene carbonate / ethyl methyl carbonate in a volume ratio of 1:1, and fluoroethylene carbonate (added at 4%); the separator was a porous glass carbon fiber membrane, and the coin cell was assembled in a glove box filled with argon gas and with a water oxygen value of less than 0.1 ppm.

[0040] like Figure 3 As shown, the charge-discharge curves of the sodium-ion battery assembled with the cathode material in the voltage range of 1.5-4.5V and at 0.1C (12mAh / g) show that the initial discharge specific capacity can reach as high as 162.87mAh / g.

[0041] like Figure 4 As shown, the capacity curve of the sodium-ion battery assembled with this cathode material after 200 cycles at a current density of 0.5C (60 mAh / g) is presented. At a current density of 0.5C, its initial reversible discharge specific capacity reaches 145.66 mAh / g, and after 200 cycles, its discharge specific capacity still reaches 101.98 mAh / g, with a capacity retention rate of 70.01%.

[0042] like Figure 5As shown, at a current density of 1C, its initial reversible discharge specific capacity can reach 101.63mAh / g, and after 300 cycles, its discharge specific capacity can still reach 81.95mAh / g, with a capacity retention rate of 76.32%.

[0043] As can be seen from the above, the sodium-ion battery cathode material Na obtained in the embodiments of the present invention... 0.70 (Fe 0.20 Co 0.20 Ni 0.20 Cu 0.03 Mn 0.20 Ti 0.21 Sodium-ion batteries assembled from high-entropy layered oxides (O2) exhibit high specific capacity and excellent long-cycle stability.

[0044] Example 2

[0045] (1) Sodium carbonate, ferric oxide, cobalt oxide, nickel oxide, copper oxide, manganese dioxide, and titanium dioxide are arranged according to the elemental composition of sodium-ion battery cathode materials. 0.7 (Fe 0.20 Co 0.20 Ni 0.20 Cu 0.06 Mn 0.20 Ti 0.18 The O2 was mixed in a certain proportion and ball-milled thoroughly to obtain a mixed powder sample with a particle size of 10-100 nm (average particle size of 50 nm);

[0046] (2) The mixed powder sample obtained in step (1) is pressed into a disc with a diameter of 14 cm using a tablet press at 17 MPa. The disc is then sintered in air at a heating rate of 5 °C / min to 700 °C for 10 h, and then sintered at a heating rate of 5 °C / min to 950 °C for 15 h. After being cooled to room temperature in the furnace, sodium-ion battery cathode material is obtained.

[0047] The sodium-ion electrode material Na obtained in this embodiment 0.7 (Fe 0.20 Co 0.20 Ni 0.20 Cu 0.06 Mn 0.20 Ti 0.18 The XRD diffraction pattern of the O2 high-entropy layered oxide conforms to the PDF card of the P2 and O3 phase structures. That is, by adjusting the ratio of copper to titanium to 1:3, the Na content in the obtained material can be determined. 0.7 (Fe 0.20 Co 0.20 Ni 0.20 Cu 0.06 Mn 0.20 Ti 0.18O2 is a mixture of P2 and O3 phases, with a ratio of 0.35:0.65 between the P2 and O3 phases.

[0048] The sodium-ion electrode material Na obtained in this embodiment 0.7 (Fe 0.20 Co 0.20 Ni 0.20 Cu 0.06 Mn 0.20 Ti 0.18 The high-entropy oxides of O2 have uniform morphology and a particle size of 0.5–5 μm.

[0049] Battery assembly: Same as in Example 1. The constant current charge-discharge performance of the assembled sodium-ion battery was tested within a voltage range of 1.5–4.5V.

[0050] The sodium-ion battery assembled with this cathode material can achieve an initial reversible discharge specific capacity of 140.36 mAh / g after 200 cycles at a current density of 0.5C (60 mAh / g). After 200 cycles, its discharge specific capacity can still reach 91.78 mAh / g, with a capacity retention rate of 65.39%.

[0051] At a current density of 1C, its initial reversible discharge specific capacity can reach 98.44mAh / g. After 300 cycles, its discharge specific capacity can still reach 75.71mAh / g, and the capacity retention rate can reach 76.91%.

[0052] Example 3

[0053] (1) Sodium carbonate, ferric oxide, cobalt oxide, nickel oxide, copper oxide, manganese dioxide, and titanium dioxide are arranged according to the elemental composition of sodium-ion battery cathode materials. 0.7 (Fe 0.20 Co 0.20 Ni 0.20 Cu 0.09 Mn 0.20 Ti 0.15 The O2 was mixed in a certain proportion and ball-milled thoroughly to obtain a mixed powder sample with a particle size of 10-100 nm (average particle size of 50 nm);

[0054] (2) The mixed powder sample obtained in step (1) is pressed into a disc with a diameter of 14 cm using a tablet press at 17 MPa. The disc is then sintered in air at a heating rate of 5 °C / min to 700 °C for 10 h, and then sintered at a heating rate of 5 °C / min to 950 °C for 15 h. After being cooled to room temperature in the furnace, sodium-ion battery cathode material is obtained.

[0055] The sodium-ion electrode material Na obtained in this embodiment 0.7 (Fe 0.20Co 0.20 Ni 0.20 Cu 0.09 Mn 0.20 Ti 0.15 The XRD diffraction pattern of the O2 high-entropy layered oxide conforms to the PDF card of the P2 and O3 phase structures. That is, by adjusting the ratio of copper to titanium to 3:5, the Na content in the obtained material can be determined. 0.7 (Fe 0.20 Co 0.20 Ni 0.20 Cu 0.09 Mn 0.20 Ti 0.15 O2 is a mixed phase of P2 and O3, with a ratio of 0.45:0.55 between the P2 and O3 phases.

[0056] The sodium-ion electrode material Na obtained in this embodiment 0.7 (Fe 0.20 Co 0.20 Ni 0.20 Cu 0.09 Mn 0.20 Ti 0.15 The high-entropy oxide of O2 has an irregular nanosheet morphology with a particle size of 0.5–5 μm.

[0057] Battery assembly: Same as in Example 1. The constant current charge-discharge performance of the assembled sodium-ion battery was tested within a voltage range of 1.5–4.5V.

[0058] The sodium-ion battery assembled with this cathode material can achieve an initial reversible discharge specific capacity of 137.25 mAh / g after 200 cycles at a current density of 0.5C (60 mAh / g). After 200 cycles, its discharge specific capacity can still reach 83.64 mAh / g, with a capacity retention rate of 60.94%.

[0059] At a current density of 1C, its initial reversible discharge specific capacity can reach 95.67mAh / g. After 300 cycles, its discharge specific capacity can still reach 70.39mAh / g, and the capacity retention rate can reach 73.57%.

[0060] As can be seen from the above, the sodium-ion battery cathode material Na obtained in the embodiments of the present invention... 0.7 (Fe 0.20 Co 0.20 Ni 0.20 Cu 0.09 Mn 0.20 Ti 0.15 Sodium-ion batteries assembled from high-entropy layered oxides (O2) exhibit high specific capacity and excellent long-cycle stability.

[0061] Example 4

[0062] (1) Sodium carbonate, ferric oxide, cobalt oxide, nickel oxide, copper oxide, manganese dioxide, and titanium dioxide are arranged according to the elemental composition of sodium-ion battery cathode materials. 0.68 (Fe 0.20 Co 0.20 Ni 0.20 Cu 0.03 Mn 0.20 Ti 0.21 The O2 was mixed in a certain proportion and ball-milled thoroughly to obtain a mixed powder sample with a particle size of 10-100 nm (average particle size of 50 nm);

[0063] (2) The mixed powder sample obtained in step (1) is pressed into a disc with a diameter of 14 cm using a tablet press at 17 MPa. The disc is then sintered in air at a heating rate of 5 °C / min to 700 °C for 10 h, and then sintered at a heating rate of 5 °C / min to 950 °C for 15 h. After being cooled to room temperature in the furnace, sodium-ion battery cathode material is obtained.

[0064] The sodium-ion electrode material Na obtained in this embodiment 0.68 (Fe 0.20 Co 0.20 Ni 0.20 Cu 0.03 Mn 0.20 Ti 0.21 The XRD diffraction pattern of the O2 high-entropy layered oxide conforms to the PDF card of the P2 and O3 phase structures. That is, by adjusting the ratio of copper to titanium to 1:7, the Na content in the obtained material can be determined. 0.68 (Fe 0.20 Co 0.20 Ni 0.20 Cu 0.03 Mn 0.20 Ti 0.21 O2 is a mixture of P2 and O3 phases, with a ratio of 0.46:0.54 between the P2 and O3 phases.

[0065] The sodium-ion electrode material Na obtained in this embodiment 0.68 (Fe 0.20 Co 0.20 Ni 0.20 Cu 0.03 Mn 0.20 Ti 0.21 The high-entropy oxides of O2 have uniform morphology and a particle size of 0.5–5 μm.

[0066] Battery assembly: Same as in Example 1. The constant current charge-discharge performance of the assembled sodium-ion battery was tested within a voltage range of 1.5–4.5V.

[0067] The sodium-ion battery assembled with this cathode material can achieve an initial reversible discharge specific capacity of 133.54 mAh / g after 200 cycles at a current density of 0.5C (60 mAh / g). After 200 cycles, its discharge specific capacity can still reach 92.43 mAh / g, with a capacity retention rate of 69.22%.

[0068] At a current density of 1C, its initial reversible discharge specific capacity can reach 91.24mAh / g. After 300 cycles, its discharge specific capacity can still reach 76.44mAh / g, with a capacity retention rate of 83.77%.

[0069] As can be seen from the above, the sodium-ion battery cathode material Na obtained in the embodiments of the present invention... 0.68 (Fe 0.20 Co 0.20 Ni 0.20 Cu 0.03 Mn 0.20 Ti 0.21 Sodium-ion batteries assembled from high-entropy layered oxides (O2) exhibit high specific capacity and excellent long-cycle stability.

[0070] Example 5

[0071] (1) Sodium carbonate, ferric oxide, cobalt oxide, nickel oxide, copper oxide, manganese dioxide, and titanium dioxide are arranged according to the elemental composition of sodium-ion battery cathode materials. 0.74 (Fe 0.20 Co 0.20 Ni 0.20 Cu 0.03 Mn 0.20 Ti 0.21 The O2 was mixed in a certain proportion and ball-milled thoroughly to obtain a mixed powder sample with a particle size of 10-100 nm (average particle size of 50 nm);

[0072] (2) The mixed powder sample obtained in step (1) is pressed into a disc with a diameter of 14 cm using a tablet press at 17 MPa. The disc is then sintered in air at a heating rate of 5 °C / min to 700 °C for 10 h, and then sintered at a heating rate of 5 °C / min to 950 °C for 15 h. After being cooled to room temperature in the furnace, sodium-ion battery cathode material is obtained.

[0073] The sodium-ion electrode material Na obtained in this embodiment 0.74 (Fe 0.20 Co 0.20 Ni 0.20 Cu 0.03 Mn 0.20 Ti 0.21The XRD diffraction pattern of the O2 high-entropy layered oxide conforms to the PDF card of the P2 and O3 phase structures. That is, by adjusting the ratio of copper to titanium to 1:7, the Na content in the obtained material can be determined. 0.74 (Fe 0.20 Co 0.20 Ni 0.20 Cu 0.03 Mn 0.20 Ti 0.21 O2 is a mixed phase of P2 and O3, with a ratio of 0.25:0.75 between the P2 and O3 phases.

[0074] The sodium-ion electrode material Na obtained in this embodiment 0.74 (Fe 0.20 Co 0.20 Ni 0.20 Cu 0.03 Mn 0.20 Ti 0.21 The high-entropy oxides of O2 have uniform morphology and a particle size of 0.5–5 μm.

[0075] Battery assembly: Same as in Example 1. The constant current charge-discharge performance of the assembled sodium-ion battery was tested within a voltage range of 1.5–4.5V.

[0076] The sodium-ion battery assembled with this cathode material can achieve an initial reversible discharge specific capacity of 149.72 mAh / g after 200 cycles at a current density of 0.5C (60 mAh / g). After 200 cycles, its discharge specific capacity can still reach 96.79 mAh / g, with a capacity retention rate of 64.64%.

[0077] At a current density of 1C, its initial reversible discharge specific capacity can reach 109.65mAh / g. After 300 cycles, its discharge specific capacity can still reach 82.95mAh / g, with a capacity retention rate of 75.89%.

[0078] As can be seen from the above, the sodium-ion battery cathode material Na obtained in the embodiments of the present invention... 0.74 (Fe 0.20 Co 0.20 Ni 0.20 Cu 0.03 Mn 0.20 Ti 0.21 Sodium-ion batteries assembled from high-entropy layered oxides (O2) exhibit high specific capacity and excellent long-cycle stability.

[0079] The preparation method disclosed in this invention allows for flexible control of the P2 and O3 phases in sodium-ion battery cathode materials through the addition of copper. By simultaneously varying the amounts of sodium, manganese, or other doping elements, the ratio of P2 to O3 in the sodium-ion battery cathode material can be changed. The provided control method only requires adjusting the amount of copper replacing titanium to achieve this change. As the proportion of copper replacing manganese increases, the sodium-ion battery cathode material transforms from a P2 phase to a P2 / O3 phase, eventually becoming entirely O3. That is, without the addition of Cu, the sodium-ion battery cathode material is in the P2 phase; when copper partially replaces titanium, both P2 and O3 phases coexist; and as the amount of copper increases, the sodium-ion battery cathode material transforms entirely into the O3 phase.

[0080] Furthermore, by regulating the local structure with Ti, the internal stress during the charging and discharging process of the material is reduced, thus improving the material's stability; the introduction of Fe increases the material's reaction potential; Mn, Co, and Cu provide charge compensation at low voltages; and the introduction of Ni increases the material's multi-electron reactions. The ratio of the P2 / O3 phase in the sodium-ion battery cathode material can be adjusted simply by controlling the elements, and by combining the advantages of multiple elements in the material, the specific capacity of this high-entropy cathode material is improved to a certain extent. After replacing a small amount of titanium with copper in the high-entropy cathode material of the sodium-ion battery, copper provides charge compensation for the sodium-ion layered oxide, and Cu... 2+ / Cu 3+ Redox couples can typically provide higher redox voltages for electrode materials and improve material stability, thereby enhancing the specific capacity and cycle stability of sodium-ion high-entropy cathode materials.

[0081] The ratio of copper to titanium is 14%–45%, ensuring a suitable P2:O3 phase ratio in the high-entropy cathode material of sodium-ion batteries, between 0.55:0.45 and 0.75:0.25. Combined with appropriate programmed heating and pressing pressure, this allows for sufficient diffusion of sodium, iron, cobalt, nickel, copper, manganese, and titanium, forming a more stable layered structure and improving the cycle stability of the sodium-ion battery. The introduction of +4 valence Ti ions disrupts the ordered arrangement of metal ions in the transition metal layer of the layered material, thereby suppressing the ordered transformation of Na+ and vacancies during charge and discharge, and lowering the diffusion barrier of Na+. Simultaneously, the ionic radius of +2 valence Cu ions is close to that of Ni2+ (60–80 pm), and copper provides charge compensation for the sodium-ion layered oxide. The Cu2+ / Cu3+ redox couple typically provides a higher redox voltage for the electrode material, thus acting as a stabilizer and reducing structural distortion and slippage of the layered material during charge and discharge. Therefore, this invention uses equal amounts of +2 valent Cu ions and +4 valent Ti ions for substitution, which will not cause Na...0.65-0.75 (Fe 0.20 Co 0.20 Ni 0.20 Cu x Mn 0.20 Ti 0.24-x) The change in the valence state of transition metals in O2 material can improve its high-voltage cycling stability. The resulting high-entropy cathode material for sodium-ion batteries has a layered structure and simultaneously contains P2 and O3 phases.

Claims

1. A method for preparing a sodium-ion battery with a high-entropy cathode material and adjustable two-phase ratio, characterized in that, Includes the following steps: S1: Sodium, iron, cobalt, nickel, manganese, and titanium sources are mixed according to the elemental composition of sodium-ion battery cathode materials. Then, according to the atomic ratio control requirements, the titanium portion is equimolarly replaced with copper, where the molar ratio of copper to titanium is within the range of 14%–45%. After thorough ball milling, a mixed powder sample is obtained with a particle size of 10–200 nm. The elemental composition of the sodium-ion battery cathode material is Na. 0.65 - 0.75 (Fe 0.2 Co 0.2 Ni 0.2 Cu x Mn y Ti 0.44-x-y O2, where 0.15≤y≤0.3, 0<x≤0.15; S2: Mix the raw materials according to the elemental composition of the regulated cathode material to obtain a raw material mixture; S3: The raw material mixture sample is pressed into tablets under 10-25 MPa conditions and then sintered at high temperature of 600-1200℃ for 10-24 hours in an atmosphere of air or oxygen, wherein the heating rate from room temperature to sintering temperature is 3-10℃ / min. Then it is cooled to room temperature to obtain sodium-ion battery cathode material with the ratio of P2 phase to O3 phase adjusted, and the ratio of P2 phase to O3 phase is between 0.45:0.55 and 0.25:0.

75. S4: The positive electrode material, conductive additive, and polyvinylidene fluoride are mixed in a mass ratio of 7:2:1, and an appropriate amount of N-methylpyrrolidone solvent is added. The positive electrode sheet is prepared through processes such as slurry mixing, coating, and drying, with an active material loading of 2-3.5 mg / cm³. -2 ; S5: The prepared positive electrode and the sodium metal negative electrode are assembled into a sodium-ion battery. The electrolyte consists of 1 mol / L NaPFO6, a mixed solvent of propylene carbonate / ethyl methyl carbonate in a volume ratio of 1:1, and 4% fluoroethylene carbonate. The separator is a porous glass carbon fiber membrane. The coin cell is assembled in a glove box filled with argon gas and the water oxygen value is below 0.1 ppm.

2. The method for preparing a sodium-ion battery with a dual-phase ratio adjustable high-entropy cathode material according to claim 1, characterized in that, The method of mixing raw materials in step S2 includes any one or a combination of at least two of the following: ball milling, co-precipitation, and sol-gel mixing.

3. The method for preparing a sodium-ion battery with a dual-phase ratio adjustable high-entropy cathode material according to claim 1, characterized in that, Sodium sources include any one or a combination of at least two of sodium carbonate, sodium citrate, sodium acetate, and sodium nitrate.

4. The method for preparing a sodium-ion battery with a dual-phase ratio adjustable high-entropy cathode material according to claim 1 or 2, characterized in that, The iron source includes any one or a combination of at least two of the following: ferric oxide, ferric oxide, ferric nitrate, and ferric acetate.

5. The method for preparing a sodium-ion battery with a dual-phase ratio adjustable high-entropy cathode material according to claim 1, characterized in that, The cobalt source includes any one or a combination of at least two of cobalt trioxide, cobalt tetroxide, cobalt citrate, and cobalt nitrate.

6. The method for preparing a sodium-ion battery with a dual-phase ratio adjustable high-entropy cathode material according to claim 1, characterized in that, The nickel source includes any one or a combination of at least two of nickel oxide, nickel hydroxide, nickel acetate, and nickel nitrate.

7. The method for preparing a sodium-ion battery with a dual-phase ratio adjustable high-entropy cathode material according to claim 1, characterized in that, The copper source includes any one or a combination of at least two of copper oxide, copper citrate, copper acetate, and copper nitrate.

8. The method for preparing a sodium-ion battery with a dual-phase ratio adjustable high-entropy cathode material according to claim 1, characterized in that, The manganese source includes any one or a combination of at least two of manganese trioxide, manganese oxide, manganese acetate, manganese nitrate, and manganese hydroxide.

9. The method for preparing a sodium-ion battery with a dual-phase ratio adjustable high-entropy cathode material according to claim 1, characterized in that, The titanium source is titanium dioxide.

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