High-entropy sodium battery positive electrode material as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of new energy, and particularly relates to a high-entropy sodium battery positive electrode material and a preparation method and application thereof. The high-entropy sodium battery positive electrode material comprises a substrate and a coating layer coating the substrate, the general formula of the matrix is NaxNiaFebMncZndTieLpO2, x is greater than or equal to 0.95 and less than or equal to 1.10, a is greater than or equal to 0.25 and less than or equal to 0.35, b is greater than or equal to 0.25 and less than or equal to 0.40, c is greater than or equal to 0.25 and less than or equal to 0.35, d is greater than 0 and less than or equal to 0.06, e is greater than 0 and less than or equal to 0.06, p is greater than or equal to 0.001 and less than or equal to 0.005, a + b + c + d + e = 1, and L comprises at least one of Cu, Mo, Sb, Sn, Nb and Li; through multi-element high-entropy doping and surface modification, the energy density, the cycling stability and the air stability of the high-entropy sodium battery positive electrode material are improved.

Description

Technical Field

[0001] This invention belongs to the field of new energy technology, specifically relating to a high-entropy sodium cathode material, its preparation method, and its application. Background Technology

[0002] Sodium-ion batteries, as an important alternative technology to lithium-ion batteries, have received widespread attention in recent years. Their core advantages lie in the abundance of sodium resources in the Earth's crust (approximately 2.36%, far exceeding lithium's 0.0017%), low cost (sodium raw material prices are only 1 / 10 to 1 / 5 of lithium), and environmental friendliness. Furthermore, sodium-ion batteries share a similar "rocking chair" working principle with lithium-ion batteries, allowing for direct adoption of mature production equipment and processes, resulting in a lower industrialization threshold. However, despite their advantages in resources and cost, sodium-ion batteries suffer from low capacity, insufficient energy density, and short cycle life, leading to high unit energy costs (yuan / Wh) that make them difficult to compete with lithium-ion batteries, severely restricting their application.

[0003] Currently, mainstream sodium-ion battery cathode materials include layered oxides (such as NaNiO2 and NaFeO2), polyanionic compounds (such as Na3V2(PO4)3), and Prussian blue analogues. Among them, NaNi... 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 layered oxides have attracted much attention due to their high theoretical capacity (≥160mAh / g) and mature preparation process, but their actual performance still suffers from low capacity and low cycle life. Summary of the Invention

[0004] Therefore, the technical problem to be solved by the present invention is to overcome the defects of existing sodium electrode materials, such as low specific capacity, low energy density and poor cycle performance, so as to provide a high-entropy sodium electrode material, its preparation method and application.

[0005] Therefore, the present invention provides the following technical solution: The first aspect of this invention protects a high-entropy sodium-ion cathode material, wherein the high-entropy sodium-ion cathode material includes a substrate and a coating layer covering the substrate; The matrix has the general formula Na. x Ni a Fe b Mn c Zn d Ti e L pO2, wherein 0.95≤x≤1.10, 0.25≤a≤0.35, 0.25≤b≤0.40, 0.25≤c≤0.35, 0<d≤0.06, 0<e≤0.06, 0.001≤p≤0.005, a+b+c+d+e=1, and L includes at least one of Cu, Mo, Sb, Sn, Nb, and Li.

[0006] According to the present invention, the general formula of the matrix is ​​Na. x Ni a Fe b Mn c Zn d Ti e L p O2, where 1.00≤x≤1.05, 0.25≤a≤0.30, 0.35≤b≤0.40, 0.25≤c≤0.30, 0.03≤d≤0.05, 0.03≤e≤0.05, 0.001≤p≤0.003, and a+b+c+d+e=1.

[0007] According to the present invention, the coating layer comprises a metal oxide.

[0008] A second aspect of this invention protects a method for preparing the aforementioned high-entropy sodium cathode material, wherein the preparation method includes the following steps: S1, sodium source, Ni ɑ Fe β Mn γ Zn ε Ti δ The (OH)2 precursor, zinc source, titanium source, and dopant are mixed and then subjected to a first sintering to obtain a sintered product; The Ni ɑ Fe β Mn γ Zn ε Ti δ (OH)₂ precursor, wherein 0.25≤α≤0.35, 0.25≤β≤0.40, 0.25≤γ≤0.35, 0≤ε≤0.02, 0≤δ≤0.02; α+β+γ+ε+δ=1; The first sintering includes three independent heating stages: a first stage, a second stage, and a third stage, and a fourth stage of cooling. In the first stage, the temperature is increased to 400-550℃ at a rate of 1-5℃ / min; in the second stage, the temperature is increased to 750-850℃ at a rate of 1-5℃ / min; and in the third stage, the temperature is increased to 950-1050℃ at a rate of 1-5℃ / min. S2, after mixing the first sintered product and the coating agent, a second sintering is carried out to obtain a high-entropy sodium cathode material.

[0009] In this invention, Ni ɑ Fe β Mn γ Zn ε Ti δ (OH)₂ precursors can be purchased or prepared. Preparation can be performed using conventional methods in the art. Typically, and non-limitingly, when Zn is 0 and Ti is 0, Ni… ɑ Fe β Mn γ The preparation method of the (OH)₂ precursor includes the following steps: dissolving a nickel source (typically, but not limited to, NiSO₄), an iron source (typically, but not limited to, FeSO₄), and a manganese source (typically, but not limited to, MnSO₄), all calculated as metal elements, in water at a molar ratio of (0.25-0.35):(0.25-0.40):(0.25-0.35) to obtain a mixed metal-containing solution with a total metal ion concentration of 2-3 mol / L, and preparing a solution with a concentration of... A 20-30 wt% ammonia solution was used to prepare a 2-3 mol / L NaOH solution. Under a nitrogen atmosphere (nitrogen flow rate 3-5 L / min), the mixed metal-containing solution and the ammonia solution were introduced concurrently into the reactor at flow rates of 8-12 L / h and 4-6 L / h, respectively, for a co-precipitation reaction. The reaction temperature was controlled at 55-60℃, and the pH of the reaction system was controlled at 10.2-10.5 using the NaOH solution. The reaction was carried out for 10-15 h. After filtration, washing, and drying, Ni was obtained. ɑ Fe β Mn γ (OH)2 precursor.

[0010] In this invention, NiSO4, FeSO4, and MnSO4 (all calculated as metallic elements) are used to prepare Ni... 1 / 3 Fe 1 / 3 Mn 1 / 3 (OH)₂, since 1 / 3 is not divisible, is also written as Ni for ease of calculation. 0.33 Fe 0.33 Mn 0.33 In the form of (OH)2, Ni should be considered... 0.33 Fe 0.33 Mn 0.33 (OH)2 also satisfies the condition that the subscript of the metal element is 1.

[0011] In this invention, the amounts of zinc source and titanium source are added according to the needs of the general formula composition of the high-entropy sodium electrode material matrix in the first part of this invention.

[0012] In this invention, sodium element in the sodium source reacts with Ni. ɑ Fe β Mn γZn ε Ti δ The molar ratio of the total metal elements in the (OH)2 precursor is 0.95-1.10:1.

[0013] According to the present invention, sodium source, Ni ɑ Fe β Mn γ Zn ε Ti δ The (OH)2 precursor, zinc source, titanium source, iron source, and dopant are mixed and then subjected to a first sintering to obtain a sintered product.

[0014] In this invention, the amount of iron source and dopant, and the type of dopant, are added according to the general formula composition of the high-entropy sodium-ion cathode material matrix in Part I of this invention.

[0015] According to the present invention, the dopant includes at least one of the following: Cu oxide, Cu sulfate, Cu chloride, Mo oxide, Mo sulfate, Mo chloride, Sb oxide, Sb sulfate, Sb chloride, Sn oxide, Sn sulfate, Sn chloride, Nb oxide, Nb sulfate, Nb chloride, Li oxide, Li sulfate, Li chloride, Li hydrochloride, and Li carbonate.

[0016] According to the present invention, the dopant includes at least one selected from the following: Cu oxide, Mo oxide, Sb oxide, Sn oxide, Nb oxide, Li hydroxide, and Li carbonate.

[0017] According to the present invention, the dopant includes at least one selected from Sb2O5, Nb2O5, CuO, MoO3, SnO2, LiOH and Li2CO3.

[0018] According to the present invention, the conditions for the first sintering include: a first stage, heating to 400-550°C at a rate of 1-5°C / min and holding for 2-5 hours; a second stage, heating to 750-850°C at a rate of 1-5°C / min and holding for 2-5 hours; a third stage, heating to 950-1050°C at a rate of 1-5°C / min and holding for 5-10 hours; and a fourth stage, cooling to 800-950°C at a rate of 2-5°C / min and holding for 8-15 hours, followed by natural cooling to room temperature (25-30°C).

[0019] In this invention, the first sintering and the second sintering are each carried out independently in an air atmosphere or an oxygen atmosphere.

[0020] According to the present invention, the coating agent comprises metal oxides and / or metal carbon oxides, and optionally, the coating agent comprises at least one of B2O3, Al2O3, ZrO2, TiO2, NiO, CaO or CaCO3.

[0021] According to the present invention, the coating agent has a mass percentage content of 0.5-3 wt% based on the mass of a calcined product.

[0022] According to the present invention, the second sintering conditions include: heating to 400-800°C at a rate of 1-5°C / min and holding at that temperature for 3-8 hours.

[0023] In this invention, after the second sintering, a sieving and iron removal step is also performed.

[0024] A third aspect of this invention protects a secondary battery, wherein the secondary battery comprises the aforementioned sodium-ion cathode material or the high-entropy sodium-ion cathode material prepared by the aforementioned preparation method.

[0025] The technical solution of this invention has the following advantages: 1. This invention provides a high-entropy sodium-ion cathode material, wherein the high-entropy sodium-ion cathode material comprises a substrate and a coating layer covering the substrate; the substrate has the general formula Na. x Ni a Fe b Mn c Zn d Ti e L p O2, wherein 0.95≤x≤1.10, 0.25≤a≤0.35, 0.25≤b≤0.40, 0.25≤c≤0.35, 0<d≤0.06, 0<e≤0.06, 0.001≤p≤0.005, a+b+c+d+e=1, and L includes at least one of Cu, Mo, Sb, Sn, Nb, and Li; the high-entropy sodium-ion battery cathode material of the present invention, through multi-element high-entropy doping and surface modification, suppresses crystal structure phase transitions and sodium precipitation side reactions, and the resulting sodium-ion battery has excellent specific capacity, energy density, cycle stability, and air stability. Furthermore, by replacing part of Ni with inexpensive Fe, the cost of raw materials is reduced while also forming Fe... 3+ / Fe 4+ Redox pairs break through the capacity bottleneck of traditional Ni-Mn based materials; although O3-type sodium nickelate has two-electron reactions (Ni 2+ / Ni 4+ Theoretically, it has a high specific capacity, but it is limited in the extraction and embedding of large-sized Na+. +This process is accompanied by a dramatic phase transition, leading to a sharp contraction and expansion of the interlayer spacing, ultimately resulting in severe local strain, cracking, and capacity decay. Therefore, this invention employs Zn, Ti, and Fe doping to regulate the material's phase transition path, exhibiting negative lattice expansion behavior during the sodium removal process (2.0-4.0V), achieving stable cycling of the high-entropy sodium cathode. Specifically, Zn doping induces the formation of a P / O symbiotic phase, causing lattice contraction under high voltage, reducing the degree of lattice expansion during sodium removal, and improving the material's specific capacity; Ti doping inhibits [Ni...] 3+ O6] Jahn-Teller distortion, eliminating Na + Hole rearrangement improves structural stability during cycling; Fe incorporation further enhances the discharge voltage plateau and increases energy density; trace L doping further improves the configuration entropy of the material system, while broadening the sodium ion diffusion channels and reducing Na+ ion density. + The migration barrier accelerates the Na + The diffusion of the coating is improved, and the cycle stability is also effectively enhanced. The coating layer can improve the air stability of the material, improve the processing performance, reduce the residual alkali on the material surface, isolate electrolyte corrosion, and reduce the occurrence of side reactions.

[0026] 2. In this invention, the general formula of the matrix is ​​further defined, wherein Ni, Fe, Mn, Zn and Ti elements constitute the high-entropy sodium cathode material. Due to the disorder of cations, the redox boundary of cations can be disturbed, the formation of harmful O'3 phase can be suppressed, and the cycle stability of the battery made of the high-entropy sodium cathode material can be significantly improved. In addition, the synergistic effect of the multi-element transition metals in the high-entropy sodium cathode material can further improve the energy density and cycle stability.

[0027] 3. This invention provides a method for preparing a high-entropy sodium-ion cathode material, wherein the preparation method includes the following steps: S1, mixing a sodium source and Ni... ɑ Fe β Mn γ Zn ε Ti δ The (OH)2 precursor, zinc source, titanium source, and dopant are mixed and then subjected to a first sintering to obtain a sintered product; the Ni ɑ Fe β Mn γ Zn ε Ti δ(OH)₂ precursor, wherein 0.25≤α≤0.35, 0.25≤β≤0.40, 0.25≤γ≤0.35, 0≤ε≤0.02, 0≤δ≤0.02; α+β+γ+ε+δ=1; the first sintering includes three independent heating stages (first stage, second stage, and third stage) and a cooling stage (fourth stage); in the first stage, the temperature is increased to 400-550℃ at a rate of 1-5℃ / min; in the second stage, the temperature is increased to 750-850℃ at a rate of 1-5℃ / min; in the third stage, the temperature is increased to 750-850℃ at a rate of 1-5℃ / min; in the third stage, the temperature is increased to 750-850℃ at a rate of 1-5℃ / min. The temperature is increased to 950-1050℃ at a rate of ℃ / min; S2, the first sintered product and the coating agent are mixed and then subjected to a second sintering to obtain a high-entropy sodium-ion cathode material; the specific precursor, zinc source and titanium source of this invention can optimize the electrochemical performance of the battery made from the high-entropy sodium-ion cathode material in terms of specific capacity and cycle life. The specific process of the first sintering, with independent heating at different stages, improves the crystal structure stability and electrochemical performance of the high-entropy sodium-ion cathode material, and avoids damage or over-reaction due to excessive temperature during the preparation of the high-entropy sodium-ion cathode material.

[0028] 4. In this invention, since the precursor with a specific content is generally prepared by coprecipitation, if Fe is excessive during the preparation process, the coprecipitation reaction is not easy to control. Therefore, an iron source is added in step S1 to further adjust the iron content in the final product. In addition, the addition of an iron source can also optimize the single crystal morphology.

[0029] 5. In this invention, the specific heating temperature, holding temperature and time of the first sintering can further reduce the internal structural defects of the high-entropy sodium cathode material, eliminate the excessive expansion and contraction of the lattice volume caused by internal stress, reduce the generation of microcracks, and further improve the cycle stability of the high-entropy sodium cathode material. Attached Figure Description

[0030] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0031] Figure 1 This is a SEM image of the high-entropy sodium-ion cathode material from Example 1; Figure 2 This is the XRD pattern of the high-entropy sodium-ion cathode material from Example 1; Figure 3 The image shows a SEM image of the sodium-ion cathode material in Comparative Example 1. Figure 4 The XRD pattern of the sodium-ion cathode material in Comparative Example 1 is shown. Figure 5 This is a specific capacity-discharge voltage diagram of the high-entropy sodium-ion cathode material of Example 1 and the sodium-ion cathode material of Comparative Example 1; Figure 6 This is a cycle count-capacity retention graph of the high-entropy sodium-ion cathode material of Example 1 and the sodium-ion cathode material of Comparative Example 1; Figure 7 This is a bar chart showing the air stability test results of the high-entropy sodium-ion cathode material of Example 1 and the sodium-ion cathode material of Comparative Example 1. Detailed Implementation

[0032] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0033] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0034] Example 1 This embodiment provides a method for preparing a high-entropy sodium-ion cathode material, including the following steps: Preparation of precursors NiSO4, FeSO4, and MnSO4 (all based on metal elements) were dissolved in water at a molar ratio of 0.3:0.4:0.3 to obtain a mixed metal-containing solution with a total metal ion concentration of 2.5 mol / L. A 25 wt% ammonia solution and a 2 mol / L NaOH solution were prepared. Under a nitrogen atmosphere at a flow rate of 4 L / min, the mixed metal-containing solution and the ammonia solution were introduced concurrently into a reactor at flow rates of 10 L / h and 5 L / h, respectively, for a co-precipitation reaction. The reaction temperature was controlled at 60 °C, and the pH of the reaction system was controlled to 10.2 by adding NaOH solution. The reaction was carried out for 12 h. After filtration, washing, and drying, Ni was obtained. 0.3 Fe 0.4 Mn 0.3 (OH)2 precursor; S1, Na2CO3 and Ni 0.3 Fe 0.4 Mn 0.3(OH)₂ precursor, ZnO, TiO₂, and Sb₂O₅ (all based on metallic elements) were mixed uniformly in a molar ratio of Na:Ni:Fe:Mn:Zn:Ti:Sb of 1:0.28:0.38:0.28:0.03:0.03:0.002. The mixture was then subjected to a first sintering process in air: In the first stage, the temperature was increased to 500℃ at a rate of 2℃ / min and held for 2 hours; in the second stage, the temperature was increased to 800℃ at a rate of 2℃ / min and held for 4 hours; in the third stage, the temperature was increased to 1000℃ at a rate of 2℃ / min and held for 8 hours; in the fourth stage, the temperature was decreased to 900℃ and held for 10 hours. After the temperature naturally decreased to room temperature, the mixture was pulverized and sieved to obtain NaNi. 0.28 Fe 0.38 Mn 0.28 Zn 0.03 Ti 0.03 Sb 0.002 O2-roasted products; S2, NaNi 0.28 Fe 0.38 Mn 0.28 Zn 0.03 Ti 0.03 Sb 0.002 The calcined product was mixed with coating agents TiO2 and ZrO2, with the mass percentages of TiO2 and ZrO2 being 0.5 wt% and 0.5 wt% respectively, based on the mass of the calcined product. After uniform mixing, the mixture was heated to 600℃ at a rate of 2℃ / min and held for 6 hours in air. After cooling to room temperature, the mixture was sieved and iron was removed to obtain a high-entropy sodium-ion cathode material. The matrix composition was NaNi. 0.28 Fe 0.38 Mn 0.28 Zn 0.03 Ti 0.03 Sb 0.002 SEM images of O2 and high-entropy sodium-ion cathode materials are shown below. Figure 1 As shown in the figure, the high-entropy sodium electrode material exhibits uniform particle size, good dispersion, and a smooth surface; the XRD pattern is as follows. Figure 2 As shown in the figure, the high-entropy sodium electrode material produced is a standard O3 phase.

[0035] Example 2 This embodiment provides a method for preparing a high-entropy sodium-ion cathode material, including the following steps: Preparation of precursors NiSO4, FeSO4, and MnSO4 (all based on metal elements) were dissolved in water at a molar ratio of 0.33:0.33:0.33 to obtain a mixed metal-containing solution with a total metal ion concentration of 3 mol / L. A 30 wt% ammonia solution and a 3 mol / L NaOH solution were prepared. Under a nitrogen atmosphere at a flow rate of 3 L / min, the mixed metal-containing solution and the ammonia solution were introduced into a reactor at concurrent flow rates of 8 L / h and 4 L / h, respectively, for a co-precipitation reaction. The reaction temperature was controlled at 55℃, and the pH of the reaction system was controlled to 10.3 by adding NaOH solution. The reaction was carried out for 10 h. After filtration, washing, and drying, Ni was obtained. 0.33 Fe 0.33 Mn 0.33 (OH)2 precursor; S1, Na2CO3 and Ni 0.33 Fe 0.33 Mn 0.33 (OH)₂ precursor, ZnO, TiO₂, Fe₂O₃, and Sb₂O₅ (all based on metallic elements) were mixed uniformly in a molar ratio of Na:Ni:Fe:Mn:Zn:Ti:Cu of 0.95:0.25:0.40:0.25:0.05:0.05:0.005. The mixture was then subjected to a first sintering process in air: In the first stage, the temperature was increased to 550℃ at a rate of 5℃ / min and held for 3 hours; in the second stage, the temperature was increased to 750℃ at a rate of 5℃ / min and held for 3 hours; in the third stage, the temperature was increased to 950℃ at a rate of 5℃ / min and held for 10 hours; in the fourth stage, the temperature was decreased to 850℃ and held for 15 hours. After the temperature naturally decreased to room temperature, the mixture was pulverized and sieved to obtain Na. 0.95 Ni 0.25 Fe 0.40 Mn 0.25 Zn 0.05 Ti 0.05 Cu 0.005 O2-roasted products; S2, put Na 0.95 Ni 0.25 Fe 0.40 Mn 0.25 Zn 0.05 Ti 0.05 Cu 0.005 O2-calcined product was mixed with coating agent CaCO3, with CaCO3 content of 1 wt% based on the mass of the calcined product. After thorough mixing, the mixture was heated to 800℃ at a rate of 5℃ / min and held for 4 hours in air. After cooling to room temperature, the mixture was sieved and iron was removed to obtain a high-entropy sodium-ion cathode material. The matrix composition was Na. 0.95 Ni 0.25 Fe 0.40 Mn 0.25 Zn0.05 Ti 0.05 Cu 0.005 O2.

[0036] Example 3 This embodiment provides a method for preparing a high-entropy sodium-ion cathode material, including the following steps: Preparation of precursors NiSO4, FeSO4, MnSO4, ZnSO4, and TiOSO4 (all based on metal elements) were dissolved in water in a molar ratio of 0.29:0.38:0.29:0.02:0.02 to obtain a mixed metal-containing solution with a total metal ion concentration of 2 mol / L. A 20 wt% ammonia solution and a 2 mol / L NaOH solution were prepared. Under a nitrogen atmosphere at a flow rate of 5 L / min, the mixed metal-containing solution and the ammonia solution were introduced into a reactor at concurrent flow rates of 12 L / h and 6 L / h, respectively, for a co-precipitation reaction. The reaction temperature was controlled at 60 °C, and the pH of the reaction system was controlled to 10.3 by adding NaOH. The reaction was carried out for 15 h. After filtration, washing, and drying, Ni was obtained. 0.29 Fe 0.38 Mn 0.29 Zn 0.02 Ti 0.02 (OH)2 precursor; S1, Na2CO3 and Ni 0.29 Fe 0.38 Mn 0.29 Zn 0.02 Ti 0.02 After uniformly mixing (OH)2 precursor, MoO3, and SnO2 (all calculated as metal elements) in a molar ratio of 1.05:0.29:0.38:0.29:0.02:0.02:0.002:0.002, the mixture was subjected to a first sintering process in air: In the first stage, the temperature was increased to 400℃ at a rate of 1℃ / min and held for 2 hours; in the second stage, the temperature was increased to 800℃ at a rate of 1℃ / min and held for 4 hours; in the third stage, the temperature was increased to 1000℃ at a rate of 1℃ / min and held for 8 hours; in the fourth stage, the temperature was decreased to 900℃ and held for 10 hours, followed by natural cooling to room temperature. After pulverization and sieving, Na was obtained. 1.05 Ni 0.29 Fe 0.38 Mn 0.29 Zn 0.02 Ti 0.02 Mo 0.002 Sn 0.002 O2-roasted products; S2, put Na 1.05 Ni 0.29 Fe 0.38 Mn0.29 Zn 0.02 Ti 0.02 Mo 0.002 Sn 0.002 O2-calcined product was mixed with coating agent Al2O3, with Al2O3 comprising 0.5 wt% of the calcined product. After uniform mixing, the mixture was heated to 500℃ at a rate of 2℃ / min and held for 6 hours in air. After cooling to room temperature, the mixture was sieved and iron was removed to obtain a high-entropy sodium-ion cathode material. The matrix composition was Na. 1.0 5Ni 0.29 Fe 0.38 Mn 0.29 Zn 0.02 Ti 0.02 Mo 0.002 Sn 0.002 O2.

[0037] Example 4 This embodiment provides a method for preparing a high-entropy sodium-ion cathode material, including the following steps: Preparation of precursors NiSO4, FeSO4, and MnSO4 (all based on metal elements) were dissolved in water at a molar ratio of 0.3:0.4:0.3 to obtain a mixed metal-containing solution with a total metal ion concentration of 2.5 mol / L. A 25 wt% ammonia solution and a 2 mol / L NaOH solution were prepared. Under a nitrogen atmosphere at a flow rate of 4 L / min, the mixed metal-containing solution and the ammonia solution were introduced concurrently into a reactor at flow rates of 10 L / h and 5 L / h, respectively, for a co-precipitation reaction. The reaction temperature was controlled at 60 °C, and the pH of the reaction system was controlled to 10.2 by adding NaOH solution. The reaction was carried out for 12 h. After filtration, washing, and drying, Ni was obtained. 0.3 Fe 0.4 Mn 0.3 (OH)2 precursor; S1, Na2CO3 and Ni 0.3 Fe 0.4 Mn 0.3 (OH)₂ precursor, ZnO, TiO₂, and Sb₂O₅ (all based on metallic elements) were mixed uniformly in a molar ratio of Na:Ni:Fe:Mn:Zn:Ti:Sb of 1.02:0.25:0.40:0.25:0.06:0.06:0.004. The mixture was then subjected to a first sintering process in air: In the first stage, the temperature was increased to 500℃ at a rate of 2℃ / min and held for 2 hours; in the second stage, the temperature was increased to 800℃ at a rate of 2℃ / min and held for 4 hours; in the third stage, the temperature was increased to 1000℃ at a rate of 2℃ / min and held for 8 hours; in the fourth stage, the temperature was decreased to 900℃ and held for 10 hours. After the temperature naturally decreased to room temperature, the mixture was pulverized and sieved to obtain Na.1.02 Ni 0.25 Fe 0.40 Mn 0.25 Zn 0.06 Ti 0.06 Sb 0.004 O2-roasted products; S2, following the procedure in step S2 of Example 1, a high-entropy sodium-ion cathode material is obtained, with the matrix composition being Na. 1.02 Ni 0.25 Fe 0.40 Mn 0.25 Zn 0.06 Ti 0.06 Sb 0.004 O2.

[0038] Example 5 This embodiment provides a method for preparing a high-entropy sodium-ion cathode material, including the following steps: The method is the same as in Example 1, except that in step S1, TiO2 is replaced with TiCl4, and the amount of TiCl4 and TiO2 is equal in molar quantity based on the element Ti, and Sb2O5 is replaced with SbCl3, and the amount of Sb2O5 and SbCl3 is equal in molar quantity based on the element Sb.

[0039] Example 6 This embodiment provides a method for preparing a high-entropy sodium-ion cathode material, including the following steps: The method is the same as in Example 1, except that in step S1, Na2CO3 and Ni are... 0.3 Fe 0.4 Mn 0.3 (OH)₂ precursor, ZnO, TiO₂, and Sb₂O₅ (all based on metal elements) were mixed uniformly in a molar ratio of Na:Ni:Fe:Mn:Zn:Ti:Sb of 1.0:0.28:0.38:0.28:0.03:0.03:0.005 to obtain a high-entropy sodium-ion cathode material. The matrix composition was NaNi. 0.28 Fe 0.38 Mn 0.28 Zn 0.03 Ti 0.03 Sb 0.005 O2.

[0040] Comparative Example 1 This comparative example provides a method for preparing a sodium-ion battery cathode material, comprising the following steps: NiSO4, FeSO4, and MnSO4 (all based on metal elements) were dissolved in water at a molar ratio of 0.33:0.33:0.33 to obtain a mixed metal-containing solution with a total metal ion concentration of 2.5 mol / L. A 25 wt% ammonia solution and a 2 mol / L NaOH solution were prepared. Under a nitrogen atmosphere at a flow rate of 4 L / min, the mixed metal-containing solution, ammonia solution, and NaOH solution were introduced concurrently into a reactor at flow rates of 10 L / h and 5 L / h, respectively, for a co-precipitation reaction. The reaction temperature was controlled at 60 °C, and the pH of the reaction system was controlled to 10.2 by adding NaOH. The reaction was carried out for 12 h. After filtration, washing, and drying, Ni was obtained. 0.33 Fe 0.33 Mn 0.33 (OH)2 precursor; S1, Na2CO3 and Ni 0.33 Fe 0.33 Mn 0.33 (OH)₂ precursors (based on metallic elements) were mixed uniformly in a molar ratio of Na:Ni:Fe:Mn of 1:0.33:0.33:0.33, and then subjected to a first sintering process in air: In the first stage, the temperature was increased to 500℃ at a rate of 2℃ / min and held for 2 hours; in the second stage, the temperature was increased to 800℃ at a rate of 2℃ / min and held for 4 hours; in the third stage, the temperature was increased to 1000℃ at a rate of 2℃ / min and held for 8 hours; in the fourth stage, the temperature was decreased to 900℃ and held for 10 hours, and then allowed to cool naturally to room temperature. After pulverization and sieving, NaNi was obtained. 0.33 Fe 0.33 Mn 0.33 O2-roasted products; S2, NaNi 0.33 Fe 0.33 Mn 0.33 The calcined product was mixed with coating agents TiO2 and ZrO2, with the mass percentages of TiO2 and ZrO2 being 0.5 wt% and 0.5 wt% respectively, based on the mass of the calcined product. After uniform mixing, the mixture was heated to 600℃ at a rate of 2℃ / min and held for 6 hours in air. After cooling to room temperature, the mixture was sieved and iron was removed to obtain the sodium-ion battery cathode material. The matrix composition was NaNi. 0.33 Fe 0.33 Mn 0.33 SEM images of O2 and sodium-ion cathode materials are shown below. Figure 3 As shown in the figure, it can be seen that the particle size of the cathode material varies greatly, its dispersibility is poor, and there are tiny particles attached to the surface. The XRD pattern is as follows. Figure 4 As shown in the figure, the prepared sodium-ion cathode material has a distinct NiO impurity phase.

[0041] Comparative Example 2 This comparative example provides a method for preparing a sodium-ion battery cathode material, comprising the following steps: The method is the same as in Example 1, except that in step S1, Na2CO3 and Ni are... 0.30 Fe 0.40 Mn 0.30 (OH)₂ precursors (based on metal elements) were mixed uniformly in a molar ratio of Na:Ni:Fe:Mn of 1:0.30:0.40:0.30 to obtain sodium-ion cathode material. The matrix composition was NaNi. 0.30 Fe 0.40 Mn 0.30 O2.

[0042] Comparative Example 3 This comparative example provides a method for preparing a sodium-ion battery cathode material, comprising the following steps: The method is the same as in Example 1, except that in step S1, Na2CO3 and Ni are... 0.3 Fe 0.4 Mn 0.3 (OH)₂ precursor, ZnO, and Sb₂O₅ (all based on metal elements) were mixed uniformly in a molar ratio of Na:Ni:Fe:Mn:Zn:Sb of 1:0.29:0.39:0.29:0.03:0.002 to obtain a sodium-ion cathode material with a matrix composition of NaNi. 0.29 Fe 0.39 Mn 0.29 Zn 0.03 Sb 0.002 O2.

[0043] Comparative Example 4 This comparative example provides a method for preparing a sodium-ion battery cathode material, comprising the following steps: The method is the same as in Example 1, except that in step S1, Na2CO3 and Ni are... 0.3 Fe 0.4 Mn 0.3 (OH)₂ precursor, TiO₂, and Sb₂O₅ (all based on metal elements) were mixed uniformly in a molar ratio of Na:Ni:Fe:Mn:Ti:Sb of 1:0.29:0.39:0.29:0.03:0.002 to obtain a sodium-ion cathode material with a matrix composition of NaNi. 0.29 Fe 0.39 Mn 0.29 Ti 0.03 Sb 0.002 O2.

[0044] Comparative Example 5 This comparative example provides a method for preparing a sodium-ion battery cathode material, comprising the following steps: The method is the same as in Example 1, except that in step S1, Na2CO3 and Ni are... 0.3 Fe 0.4 Mn 0.3 (OH)₂ precursor, ZnO, and TiO₂ (all based on metal elements) were mixed uniformly in a molar ratio of Na:Ni:Fe:Mn:Zn:Ti of 1:0.28:0.38:0.28:0.03:0.03 to obtain a sodium-ion cathode material. The matrix composition was NaNi. 0.28 Fe 0.38 Mn 0.28 Zn 0.03 Ti 0.03 O2.

[0045] Comparative Example 6 This comparative example provides a method for preparing a high-entropy sodium-ion cathode material, comprising the following steps: Following the method of Example 1, the only difference is that the amount of ZnO and TiO2 added is adjusted to obtain a high-entropy sodium-ion cathode material, with the matrix composition being NaNi. 0.25 Fe 0.30 Mn 0.25 Zn 0.1 Ti 0.1 Sb 0.002 O2.

[0046] Comparative Example 7 This comparative example provides a method for preparing a high-entropy sodium-ion cathode material, comprising the following steps: The method is the same as in Example 1, except that NaNi is obtained. 0.28 Fe 0.38 Mn 0.28 Zn 0.03 Ti 0.03 Sb 0.002 After calcination with O2, step S2 was not performed, resulting in a high-entropy sodium-ion cathode material with a matrix composition of NaNi. 0.28 Fe 0.38 Mn 0.28 Zn 0.03 Ti 0.0 3Sb 0.002 O2.

[0047] Comparative Example 8 This comparative example provides a method for preparing a sodium-ion battery cathode material, comprising the following steps: The process is the same as in Example 1, except that in step S1, the first sintering is performed in an air atmosphere: in the first stage, the temperature is increased to 500°C at a rate of 2°C / min and held for 4 hours; in the second stage, the temperature is increased to 1000°C at a rate of 2°C / min and held for 8 hours to obtain a high-entropy sodium-ion cathode material, with the same substrate as in Example 1.

[0048] Test case Preparation method of CR2032 button cell: The materials (high-entropy sodium-ion cathode material or sodium-ion cathode material) obtained in the examples and comparative examples are used as cathode active materials. These are mixed with polyvinylidene fluoride and carbon black in a mass ratio of 95:2.5:2.5, and N-methylpyrrolidone (NMP) is added to obtain a cathode slurry. The solid content of the cathode slurry is 52%. The slurry is then homogenized and coated, and the compaction density of the electrode sheet is 3.2 g / cm³. 3 The electrode was fabricated using a lithium metal sheet as the counter electrode and a glass fiber separator. A 1 mol / L lithium hexafluorophosphate solution of ethylene carbonate (EC) and dimethyl carbonate (DMC) (EC to DMC volume ratio of 1:1) was used as the electrolyte. The CR2032 coin cell was assembled in an argon-filled glove box and then placed in the Blue Electric Test System for electrical performance testing.

[0049] Test method for charge and discharge capacity: Charge the battery to 4.0V at a rate of 0.1C, and obtain the 0.1C charge specific capacity according to the battery mass; then discharge the battery to 2.0V at a rate of 0.1C, and obtain the 0.1C discharge specific capacity according to the battery mass.

[0050] The test method for capacity retention rate is as follows: At 25°C, the battery is charged to 4.0V at a rate of 1C and then discharged to 2.0V at a rate of 1C. This cycle is repeated 50 times. The capacity retention rate on the 50th cycle is calculated as (discharge capacity on the 50th cycle / discharge capacity on the 1st cycle) × 100%.

[0051] The discharge energy density at 0.1C = discharge specific capacity at 0.1C × discharge voltage at 0.1C, which can be directly read by the Blue Electric testing software.

[0052] The test results are shown in Table 1; Table 1

[0053] As shown in the table, the high-entropy sodium-ion cathode material prepared in this invention exhibits excellent charge-discharge capacity and cycle performance, with a specific capacity greater than 160 mAh / g at 0.1C charging and a capacity retention rate greater than 90% after 50 cycles. Using Ni and Fe as the main active elements, through Ni... 2+ / Ni 3+ / Ni 4+ Fe 3+ / Fe 4+ Multi-electron reactions in dual-active elements enhance specific capacity; doping with small amounts of inactive elements Zn and Ti widens the interlayer spacing, accelerates sodium ion diffusion, and inhibits Mn. 3+The Jahn-Teller distortion stabilizes the crystal structure and further activates the redox activity of Ni / Fe ions; the dopant enhances electronic conductivity and reduces interfacial impedance.

[0054] In contrast, in Comparative Example 1, there is a traditional NaNi without Fe, Zn, Ti, and L. 0.33 Fe 0.33 Mn 0.33 The O2 material exhibits a poor charging specific capacity of only 152.3 mAh / g and a capacity retention rate of only 70.3%. While increasing the Fe content did increase the specific capacity of the cathode material in Comparative Example 2, the Fe content... 3+ The Jahn-Teller distortion was severe, affecting the material's structural stability, resulting in a capacity retention of only 67.1%. Furthermore, while single Zn and Ti doping, or the absence of Sb, Mo, Cu, and Sn doping, improved specific capacity and cycle performance, they failed to achieve optimal performance. Excessive Zn and Ti doping also reduced battery performance. While cathode materials doped with only Ti or Cu showed improved specific capacity and cycle performance, they did not meet the required specifications. In Comparative Example 5, the addition of excessive Ti led to Na... + It is difficult to fully intercalate and deintercalate, resulting in a gradual decrease in capacity. In addition, the coating layer can prevent the active material from reacting with the electrolyte, thereby improving the cycling stability of the material.

[0055] The first sintering process, with its specific temperature rise, can reduce lattice stress and promote uniform element distribution. In contrast, in Comparative Example 8, the material generates more internal stress due to improper sintering process, making it prone to deformation during charging and discharging, which in turn damages the material's cycle performance.

[0056] from Figure 5 It can be seen that, under the same discharge voltage, the high-entropy sodium cathode material in Example 1 has a higher specific capacity and voltage than that in Comparative Example 1; this means that Example 1 has a higher energy density; and Comparative Example 1 has a clear discharge plateau at 2.5V, which is often accompanied by irreversible phase transitions of the material, meaning that the material structure of Comparative Example 1 has poor reversibility.

[0057] from Figure 6 It can be seen that the high-entropy sodium-ion cathode material of Example 1 still retains more than 90% of its capacity after 50 cycles, while the sodium-ion cathode material of Comparative Example 1 only retains about 70% of its capacity after 50 cycles.

[0058] Air stability test method: The moisture content of the cathode materials prepared in the examples and comparative examples was detected by Karl Fischer moisture analyzer under the conditions of temperature of 25°C and air humidity of 40%. The moisture content was tested at 0 days, 3 days, 5 days, 7 days and 14 days.

[0059] Depend on Figure 7 It can be seen that, compared with Comparative Example 1, the high-entropy sodium-ion cathode material of Example 1 showed less increase in moisture content after 14 days under the conditions of 25°C and 40% air humidity. The moisture content of Example 1 was only 2037 ppm, compared with 3576 ppm in Comparative Example 1, demonstrating excellent air stability.

[0060] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A high-entropy sodium cathode material, characterized in that, The high-entropy sodium-ion cathode material includes a matrix and a coating layer covering the matrix; The matrix has the general formula Na. x Ni a Fe b Mn c Zn d Ti e L p O2, wherein 0.95≤x≤1.10, 0.25≤a≤0.35, 0.25≤b≤0.40, 0.25≤c≤0.35, 0<d≤0.06, 0<e≤0.06, 0.001≤p≤0.005, a+b+c+d+e=1, and L includes at least one of Cu, Mo, Sb, Sn, Nb, and Li.

2. The high-entropy sodium cathode material according to claim 1, characterized in that, The matrix has the general formula Na. x Ni a Fe b Mn c Zn d Ti e L p O2, where 1.00≤x≤1.05, 0.25≤a≤0.30, 0.35≤b≤0.40, 0.25≤c≤0.30, 0.03≤d≤0.05, 0.03≤e≤0.05, 0.001≤p≤0.003, a+b+c+d+e=1; And / or, the coating layer comprises a metal oxide.

3. A method for preparing the high-entropy sodium cathode material as described in claim 1 or 2, characterized in that, The preparation method includes the following steps: S1, sodium source, Ni ɑ Fe β Mn γ Zn ε Ti δ The (OH)2 precursor, zinc source, titanium source, and dopant are mixed and then subjected to a first sintering to obtain a sintered product; The Ni ɑ Fe β Mn γ Zn ε Ti δ In the (OH)2 precursor; 0.25≤ɑ≤0.35, 0.25≤β≤0.40, 0.25≤γ≤0.35, 0≤ε≤0.02, 0≤δ≤0.02; ɑ+β+γ+ε+δ=1; The first sintering includes three independent heating stages: a first stage, a second stage, and a third stage, and a fourth stage of cooling. In the first stage, the temperature is increased to 400-550℃ at a rate of 1-5℃ / min; in the second stage, the temperature is increased to 750-850℃ at a rate of 1-5℃ / min; and in the third stage, the temperature is increased to 950-1050℃ at a rate of 1-5℃ / min. S2, after mixing the first sintered product and the coating agent, a second sintering is carried out to obtain a high-entropy sodium cathode material.

4. The preparation method according to claim 3, characterized in that, Sodium source, Ni ɑ Fe β Mn γ Zn ε Ti δ The (OH)2 precursor, zinc source, titanium source, iron source, and dopant are mixed and then subjected to a first sintering to obtain a sintered product.

5. The preparation method according to claim 3 or 4, characterized in that, The dopant includes at least one of the following: Cu oxide, Cu sulfate, Cu chloride, Mo oxide, Mo sulfate, Mo chloride, Sb oxide, Sb sulfate, Sb chloride, Sn oxide, Sn sulfate, Sn chloride, Nb oxide, Nb sulfate, Nb chloride, Li oxide, Li sulfate, Li chloride, Li hydrochloride, and Li carbonate.

6. The preparation method according to claim 5, characterized in that, The dopant includes at least one of the following: Cu oxide, Mo oxide, Sb oxide, Sn oxide, Nb oxide, Li hydroxide, and Li carbonate.

7. The preparation method according to claim 3, characterized in that, The conditions for the first sintering include: a first stage, heating to 400-550℃ at a rate of 1-5℃ / min and holding for 2-5 hours; a second stage, heating to 750-850℃ at a rate of 1-5℃ / min and holding for 2-5 hours; a third stage, heating to 950-1050℃ at a rate of 1-5℃ / min and holding for 5-10 hours; and a fourth stage, cooling to 800-950℃ at a rate of 2-5℃ / min and holding for 8-15 hours, followed by natural cooling to room temperature.

8. The preparation method according to claim 3, characterized in that, The coating agent includes metal oxides and / or metal carbon oxides; And / or, based on the mass percentage of a calcined product, the coating agent is 0.5-3 wt%.

9. The preparation method according to claim 3, characterized in that, The second sintering conditions include: heating to 400-800℃ at a rate of 1-5℃ / min and holding at that temperature for 3-8 hours.

10. A secondary battery, characterized in that, The secondary battery comprises the high-entropy sodium-ion cathode material as described in claim 1 or 2, or the high-entropy sodium-ion cathode material prepared by the preparation method described in any one of claims 3-9.

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