A sodium battery positive electrode material with high capacity and high rate performance, a preparation method and application thereof

Abstract

The application relates to a high-capacity high-rate sodium battery positive electrode material and a preparation method and application thereof. x Cu a Zn b Ni c Fe d Al e Mn f Ti g M h O 2±α ; M is an element with an atomic number less than or equal to 20, and at least contains a Mg element; the sodium battery positive electrode material is a layered oxide material, the space group is R-3m, and the corresponding structure is an O3 phase; x, a, b, c, d, e, f, g, h and 2+alpha are respectively the mole percentages of corresponding elements, the components in the chemical formula satisfy charge conservation and stoichiometric ratio conservation, namely, x+2x(a+b+c)+3x(d+e)+4x(f+g)+kxh=2x(2+alpha) and a+b+c+d+e+f+g+h=1, wherein k is the average chemical valence of the element M, and 0.9<=x<=1.03, 0 The Zn element is distributed in a concentration gradient on the surface of the sodium battery positive electrode material, and the surface of the sodium battery positive electrode material also has an island-shaped alumina coating structure.

Description

Technical Field

[0001] This invention relates to the field of layered oxide technology for sodium-ion batteries, and particularly to a high-capacity, high-rate performance sodium-ion battery cathode material, its preparation method, and its applications. Background Technology

[0002] Currently, the energy density of sodium-ion batteries remains relatively low compared to lithium-ion batteries, which is one of the pain points of sodium-ion batteries. Cathode materials play a crucial role in improving energy density. Currently, the charging cut-off voltage of Ni-Fe-Mn-based and Cu-Ni-Fe-Mn-based bulk oxide cathodes used in industry is below 4V, and their specific capacity is typically below 140mAh / g, which is detrimental to improving the energy density of sodium-ion batteries. The commonly used Ni-Fe-Mn-based materials exhibit significant volume strain when charged to high voltages, leading to irreversible phase transitions and causing cracking in the material bulk. Common coating methods are insufficient to prevent the accumulation of strain within the bulk phase, and the coating process increases production costs and time. Simultaneously, at high voltages, Fe migration is severe, and Ni and Mn dissolve during cycling. Therefore, the disadvantages of traditional materials are amplified at high voltages.

[0003] High-entropy strategies have emerged as a prominent modification method for sodium-ion layered oxide cathodes, improving irreversible phase transitions during charge-discharge processes and reducing volumetric strain and cracking during cycling due to their multi-element effects. However, reports on high-entropy O3-type Na layered cathodes with high energy density remain limited. High-entropy oxides typically contain multiple inert elements to achieve high configurational entropy, with each element usually exceeding 0.1 mol. Consequently, low content of variable-valence elements (e.g., Ni < 0.2) or excessive presence of heavy elements (e.g., Sn) leads to reduced specific capacity. Furthermore, element selection is limited, typically focusing on a few elements such as Mg, Ni, Cu, Zn, Fe, Co, Ti, Mn, Sn, and Sb. Due to high cost and low crustal abundance, Co is best avoided or used sparingly as a dopant in sodium-ion batteries. Excessive use of Mg and Zn reduces the solid solubility of Ni, thus decreasing specific capacity. During cycling, Sn incorporation leads to initial capacity loss and post-cycling elemental segregation, hindering its large-scale application. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing technologies by providing a high-capacity, high-rate sodium-ion cathode material, its preparation method, and its applications. This material can achieve a reversible phase transition under high voltage and can suppress cracking during material cycling, thus significantly improving the material's capacity retention rate.

[0005] To achieve the above objectives, in a first aspect, the present invention provides a high-capacity, high-rate performance sodium-ion cathode material with the chemical formula Na. x Cu a Zn b Ni c Fe d Al e Mn f Ti g M h O 2±α Cu, Zn, Ni, Fe, Mn, and Ti are transition metal elements; Al is a light metal element with atomic number 13; M is an element with atomic number less than or equal to 20, and must contain at least Mg.

[0006] The sodium-ion cathode material is a layered oxide material with space group R-3m and corresponding structure O3 phase; x, a, b, c, d, e, f, g, h and 2±α are the molar percentages of the corresponding elements, and each component in the chemical formula satisfies charge conservation and stoichiometric ratio conservation, that is, x+2×(a+b+c)+3×(d+e)+4×(f+g)+k×h=2×(2±α) and a+b+c+d+e+f+g+h=1, where k is the average chemical valence state of element M, and 0.9≤x≤1.03, 0<a<0.1, 0<b<0.05, 0.33<c≤0.4, 0.05<d<0.15, 0<e<0.03, 0.2≤f≤0.3, 0<g≤0.2, 0<h≤0.05, 0≤α≤0.05;

[0007] The Zn element exhibits a concentration gradient distribution on the surface of the sodium-ion battery cathode material, and the surface of the sodium-ion battery cathode material also has an island-like coating structure of aluminum oxide.

[0008] Preferably, the sodium-ion cathode material is used as the positive electrode active material for sodium-ion secondary batteries.

[0009] Secondly, embodiments of the present invention provide a method for preparing the sodium-ion cathode material described in the first aspect above, wherein the preparation method is a solid-state method, comprising:

[0010] According to the required stoichiometric ratio, excess 0%-10wt% of sodium source, the required stoichiometric amounts of copper source, zinc source, nickel source, iron source, aluminum source, manganese source, titanium source and M-containing precursor are mixed in proportion, anhydrous ethanol, isopropanol or acetone are added, and the mixture is ball-milled at 100-700 rpm for 1-12 hours to obtain powder.

[0011] The obtained powder is placed in a crucible and sintered in an atmosphere of air or pure oxygen. It is calcined at 800-1100℃ for 1-20 hours, cooled to room temperature, and then ground to obtain a layered oxide cathode material for sodium-ion batteries, which is the sodium battery cathode material.

[0012] The sodium source includes at least one of sodium hydroxide, sodium carbonate, sodium nitrate, sodium oxide, sodium peroxide, sodium acetate, and sodium oxalate.

[0013] The copper source, zinc source, nickel source, iron source, aluminum source, manganese source, and titanium source respectively include at least one of the following: metal oxides, metal carbonates, metal nitrates, metal oxalates, metal acetates, metal sulfates, and metal hydroxides containing copper, zinc, nickel, iron, aluminum, manganese, and titanium.

[0014] The precursor containing M includes at least one of the following: oxides, carbonates, nitrates, oxalates, acetates, sulfates, and hydroxides containing M; M is an element with an atomic number less than or equal to 20, and contains at least Mg.

[0015] Thirdly, embodiments of the present invention provide a method for preparing the sodium-ion cathode material described in the first aspect above, wherein the preparation method is a sol-gel method, comprising:

[0016] According to the required stoichiometric ratio, an excess of 0%-10wt% sodium source, the required stoichiometric amounts of copper source, zinc source, nickel source, iron source, aluminum source, manganese source, titanium source, precursor containing M, and an appropriate amount of citric acid are dissolved in deionized water to form a mixed solution.

[0017] The resulting mixed solution was evaporated at a constant temperature in an oil bath to form a gel;

[0018] The obtained gel is placed in a crucible and pretreated at 300-600℃ for 1-20 hours. The powder obtained after pretreatment is then ground and placed in a crucible. It is then sintered at 800-1100℃ in an air or oxygen atmosphere for 1-20 hours. After cooling to room temperature, it is ground in an inert atmosphere to obtain a layered oxide cathode material for sodium-ion batteries, which is the sodium battery cathode material.

[0019] The sodium source, copper source, zinc source, nickel source, iron source, aluminum source, manganese source, titanium source, and precursor containing M respectively include: soluble salts containing sodium, copper, zinc, nickel, iron, aluminum, manganese, titanium, and M.

[0020] The soluble salt includes at least one of the following: nitrate, oxalate, acetate, or sulfate of the corresponding metal; M is an element with an atomic number less than or equal to 20, and contains at least Mg.

[0021] Fourthly, embodiments of the present invention provide a method for preparing the sodium-ion cathode material described in the first aspect above, wherein the preparation method is a co-precipitation-solid phase method, comprising:

[0022] The Ni-Fe-Mn precursor was obtained by co-precipitation, specifically as follows: Na x Cu a Zn b Ni c Fe d Al e Mn f Ti g M h O 2±α A deionized aqueous solution of NiSO4·6H2O, FeSO4·7H2O, and MnSO4·H2O sulfates, i.e., a transition metal solution, was prepared according to the stoichiometric ratio. An alkaline solution was prepared using sodium hydroxide, ammonia, and deionized water. An appropriate amount of deionized water was added to the reaction vessel, and nitrogen gas was introduced. The mixture was heated and kept at a constant temperature. Then, while stirring, the transition metal solution and the alkaline solution were added dropwise, and the pH was maintained between 11.3 and 11.8. After the reaction was completed, the precipitate was filtered, washed, and dried to obtain a Ni-Fe-Mn precursor with uniform elemental distribution.

[0023] According to the required stoichiometric ratio, an excess of 0%-10wt% sodium source, the required stoichiometric amount of Ni-Fe-Mn precursor, copper source, zinc source, aluminum source, titanium source and M-containing precursor are mixed and ball-milled for 1-20 hours, and sintered at 800℃-1100℃ for 1-20 hours in air or oxygen atmosphere to obtain sodium-ion battery layered oxide cathode material, which is the sodium battery cathode material mentioned above.

[0024] The sodium source includes one or more of sodium hydroxide, sodium carbonate, sodium nitrate, sodium oxide, sodium peroxide, and sodium oxalate.

[0025] The copper source, zinc source, aluminum source, and titanium source each include at least one of the following: metal oxides, metal carbonates, metal nitrates, metal oxalates, metal acetates, metal sulfates, and metal hydroxides containing copper, zinc, aluminum, and titanium.

[0026] The precursor containing M includes at least one of the following: oxides, carbonates, nitrates, oxalates, acetates, sulfates, and hydroxides containing M; M is an element with an atomic number less than or equal to 20, and contains at least Mg.

[0027] Fifthly, embodiments of the present invention provide a sodium-ion secondary battery electrode material, comprising: a conductive additive, a binder, and the high-capacity, high-rate performance sodium-ion positive electrode material described in the first aspect above.

[0028] Preferably, the conductive additive includes at least one of carbon black, acetylene black, graphite powder, carbon nanotubes, graphene, and nitrogen-doped carbon.

[0029] The adhesive includes at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), sodium alginate, sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR).

[0030] Sixthly, embodiments of the present invention provide a positive electrode sheet for a sodium-ion secondary battery electrode material.

[0031] In a seventh aspect, embodiments of the present invention provide a sodium-ion secondary battery comprising the positive electrode sheet described in the sixth aspect above.

[0032] The high-capacity, high-rate performance sodium-ion battery cathode material provided in this invention utilizes only elements with atomic numbers less than or equal to 30 for high-entropy design, avoiding the use of heavier elements. By controlling the Ti content and the selection of dopant element M, the migration of Fe during charging is suppressed. Simultaneously, the use of smaller amounts of Zn, Mg, and Al avoids the precipitation of other oxide impurities due to solid solubility. The rational use of nickel as a charge compensation element helps improve the electrochemical performance of the cathode at high cutoff voltages. The concentration gradient of zinc on the surface and the coating effect of aluminum oxide formed by the difference in solid solubility stabilize the material surface. By adjusting the bonding between the transition metal and oxygen in the sodium-ion layered oxide cathode material, a high-capacity, high-rate performance sodium-ion battery cathode material can be obtained. Attached Figure Description

[0033] Figure 1 The X-ray diffraction (XRD) patterns of the layered oxide cathode materials prepared in Examples 1-3 and Comparative Example 1 of this invention are shown below.

[0034] Figure 2 This is a scanning electron microscope (SEM) image of the layered oxide cathode material prepared in Example 1 of the present invention;

[0035] Figure 3 Aberration-corrected scanning transmission electron microscope (AC-STEM) image of the layered oxide cathode material prepared in Example 1 of this invention.

[0036] Figure 4 a is an elemental composition distribution diagram (STEM-EDS mapping) of the layered oxide cathode material prepared in Example 1 of this invention.

[0037] Figure 4 b is an elemental composition diagram of the layered oxide cathode material prepared in Example 1 of this invention;

[0038] Figure 5 The specific capacity-cycle curve of a sodium-ion half-cell assembled with the layered oxide cathode material prepared in Example 1 of the present invention during the first 100 cycles under 1C / 1C, 2-4.2V conditions.

[0039] Figure 6 The specific capacity-cycle curve of a sodium-ion half-cell assembled with the layered oxide cathode material prepared in Example 1 of this invention during the first 1000 cycles under 3C / 3C, 2-4.1V conditions.

[0040] Figure 7 The specific capacity-cycle curve of a sodium-ion half-cell assembled with the layered oxide cathode material prepared in Example 1 of this invention during the first 1000 cycles under 5C / 5C, 2-4.1V conditions.

[0041] Figure 8 The specific capacity-voltage diagram of a sodium-ion half-cell assembled with the layered oxide cathode material prepared in Example 1 of this invention during the first 3 weeks of testing under 0.1C / 0.1C, 2-4.1V conditions;

[0042] Figure 9 The rate performance of a sodium-ion half-cell assembled from the layered oxide cathode material prepared in Example 1 of this invention is shown in the figure, tested under conditions of 2-4.1V. Detailed Implementation

[0043] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0044] This invention addresses the shortcomings of existing Ni-Fe-Mn based materials by proposing a novel high-entropy strategy. It utilizes only elements with atomic numbers less than or equal to 30 for high-entropy design, thereby achieving a high-capacity, high-rate performance sodium-ion cathode material, its preparation method, and its applications.

[0045] The high-capacity, high-rate performance sodium-ion battery cathode material provided in this invention has the chemical formula Na. x Cu a Zn b Ni c Fe d Al e Mn f Ti g M h O 2±α Cu, Zn, Ni, Fe, Mn, and Ti are transition metal elements; Al is a light metal element with atomic number 13; M is an element with atomic number less than or equal to 20, and must contain at least Mg.

[0046] The sodium-ion battery cathode material is a layered oxide material with space group R-3m, corresponding to an O3 phase structure. x, a, b, c, d, e, f, g, h, and 2±α represent the molar percentages of the corresponding elements. The components in the chemical formula satisfy charge conservation and stoichiometry conservation, i.e., x + 2×(a+b+c) + 3×(d+e) + 4×(f+g) + k×h = 2×(2±α) and a + b + c + d + e + f + g + h = 1, where k is the average chemical valence state of element M, and 0.9 ≤ x ≤ 1.03, 0 < a < 0.1, 0 < b < 0.05, 0.33 < c ≤ 0.4, 0.05 < d < 0.15, 0 < e < 0.03, 0.2 ≤ f ≤ 0.3, 0 < g ≤ 0.2, 0 < h ≤ 0.05, and 0 ≤ α ≤ 0.05.

[0047] Zn exhibits a concentration gradient on the surface of sodium-ion battery cathode materials. This concentration gradient is highest near the surface (around 10 nm) and lowest in the bulk phase. It gradually decreases from the surface inwards, reaching a concentration roughly the same as the bulk phase below 10 nm. This distribution depends on the fact that the solid solubility of the controlled divalent elements (Zn, Ni, Mg, Cu) has reached its limit, leading to a tendency for substances to precipitate on the surface. We observed higher concentrations of zinc-containing substances and lower concentrations of nickel on the surface. Zinc is electrochemically inert, while nickel is electrochemically active. Thus, during charge-discharge processes, the tendency for cations to change valence is reduced on the surface, resulting in lower surface stress and inhibiting cracking. This is one of the reasons for its good cycle stability.

[0048] The sodium-ion battery cathode material also exhibits an island-like coating structure of alumina on its surface. Aluminum has low solid solubility in the designed sodium-ion battery oxide, and the alumina raw material used has a particle size of tens of nanometers. Therefore, it cannot completely dissolve into the bulk phase and continues to adhere to the surface as alumina, forming some island-like coatings. This reduces side reactions between the electrolyte and the surface, which helps improve cycle performance.

[0049] The sodium-ion cathode material of the present invention is used as the positive electrode active material for sodium-ion secondary batteries.

[0050] The sodium-ion battery cathode material of the present invention, namely the layered oxide material for sodium-ion batteries, can be prepared by any of the following methods: solid-state method, sol-gel method, or co-precipitation-solid-state method.

[0051] Preparation method 1: Solid-state method, including:

[0052] S11, according to the required stoichiometric ratio, mix an excess of 0%-10wt% sodium source, the required stoichiometric amounts of copper source, zinc source, nickel source, iron source, aluminum source, manganese source, titanium source and M-containing precursor in proportion, add anhydrous ethanol, isopropanol or acetone, and ball mill at 100-700 rpm for 1-12 hours to obtain powder.

[0053] S12, the obtained powder is placed in a crucible and sintered in an atmosphere of air or pure oxygen. It is calcined at 800-1100℃ for 1-20 hours, cooled to room temperature, and then ground to obtain a layered oxide cathode material for sodium-ion batteries, which is the sodium battery cathode material.

[0054] The sodium source includes at least one of sodium hydroxide, sodium carbonate, sodium nitrate, sodium oxide, sodium peroxide, sodium acetate, and sodium oxalate.

[0055] The copper source, zinc source, nickel source, iron source, aluminum source, manganese source, and titanium source respectively include at least one of the following: metal oxides, metal carbonates, metal nitrates, metal oxalates, metal acetates, metal sulfates, and metal hydroxides containing copper, zinc, nickel, iron, aluminum, manganese, and titanium.

[0056] The precursor containing M includes at least one of the following: oxides, carbonates, nitrates, oxalates, acetates, sulfates, and hydroxides containing M; M is an element with an atomic number less than or equal to 20, and contains at least Mg.

[0057] Preparation method two: Sol-gel method, including:

[0058] S21, according to the required stoichiometric ratio, dissolve an excess of 0%-10wt% sodium source, the required stoichiometric amounts of copper source, zinc source, nickel source, iron source, aluminum source, manganese source, titanium source, M-containing precursor, and an appropriate amount of citric acid in deionized water to form a mixed solution.

[0059] S22, the resulting mixed solution is evaporated at a constant temperature in an oil bath to form a gel;

[0060] S23. Place the obtained gel in a crucible and pretreat it at 300-600℃ for 1-20 hours. Then grind the pretreated powder and place it in a crucible. Sinter it at 800-1100℃ in an air or oxygen atmosphere for 1-20 hours. After cooling to room temperature, grind it in an inert atmosphere to obtain the sodium-ion battery layered oxide cathode material, which is the sodium battery cathode material.

[0061] Among them, the sodium source, copper source, zinc source, nickel source, iron source, aluminum source, manganese source, titanium source, and precursor containing M respectively include: soluble salts containing sodium, copper, zinc, nickel, iron, aluminum, manganese, titanium and M.

[0062] Soluble salts include at least one of the following: nitrate, oxalate, acetate, or sulfate of the corresponding metal; M is an element with an atomic number less than or equal to 20, and contains at least Mg.

[0063] Preparation method three: coprecipitation-solid phase method, including:

[0064] S31, the Ni-Fe-Mn precursor was obtained by co-precipitation, specifically: according to the molecular formula Na x Cu a Zn b Ni c Fe d Al e Mn f Ti g M h O 2±α A deionized aqueous solution of NiSO4·6H2O, FeSO4·7H2O, and MnSO4·H2O sulfates, i.e., a transition metal solution, was prepared according to the stoichiometric ratio. An alkaline solution was prepared using sodium hydroxide, ammonia, and deionized water. An appropriate amount of deionized water was added to the reaction vessel, and nitrogen gas was introduced. The mixture was heated and kept at a constant temperature. Then, while stirring, the transition metal solution and the alkaline solution were added dropwise, and the pH was maintained between 11.3 and 11.8. After the reaction was completed, the precipitate was filtered, washed, and dried to obtain a Ni-Fe-Mn precursor with uniform elemental distribution.

[0065] In one specific embodiment, the concentration of the transition metal solution was 2 mol / L, the concentration of sodium hydroxide in the alkaline solution was 4 mol / L, the concentration of ammonia was 1 mol / L, the heating temperature in the reactor was 70°C, and the stirring speed was 1000 r / min. The drying conditions were 120°C for 5 hours.

[0066] The specific data above is merely data from a specific embodiment that can implement the present invention, used to help understand the implementation of the technical solution of the present invention. Those skilled in the art will understand that this illustrative data is not intended to limit the present invention to using only the above parameter values.

[0067] S32, according to the required stoichiometric ratio, an excess of 0%-10wt% sodium source, the required stoichiometric Ni-Fe-Mn precursor, copper source, zinc source, aluminum source, titanium source and M-containing precursor are mixed and ball-milled for 1-20 hours, and sintered at 800℃-1100℃ for 1-20 hours in air or oxygen atmosphere to obtain sodium-ion battery layered oxide cathode material, which is sodium battery cathode material.

[0068] The sodium source includes one or more of sodium hydroxide, sodium carbonate, sodium nitrate, sodium oxide, sodium peroxide, and sodium oxalate.

[0069] The copper source, zinc source, aluminum source, and titanium source each include at least one of the following: metal oxides, metal carbonates, metal nitrates, metal oxalates, metal acetates, metal sulfates, and metal hydroxides containing copper, zinc, aluminum, and titanium.

[0070] The precursor containing M includes at least one of the following: oxides, carbonates, nitrates, oxalates, acetates, sulfates, and hydroxides containing M; M is an element with an atomic number less than or equal to 20, and contains at least Mg.

[0071] The sodium-ion battery layered oxide material proposed above or prepared by the above method can be used in the electrode material of sodium-ion secondary batteries. For example, it can be used together with conductive additives and binders to form the positive electrode material of sodium-ion secondary batteries.

[0072] The compatible conductive additives include at least one of the following: carbon black, acetylene black, graphite powder, carbon nanotubes, graphene, and nitrogen-doped carbon; the binders include at least one of the following: polyvinylidene fluoride (PVDF), sodium alginate, sodium carboxymethyl cellulose (CMC-Na), and styrene-butadiene rubber (SBR).

[0073] Sodium-ion batteries prepared using the above-mentioned sodium-ion secondary battery cathode material have high reversible discharge specific capacity and high high-voltage cycle stability, and can maintain a high cycle retention rate even under long-term cycling at high voltage.

[0074] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0075] Example 1

[0076] This embodiment employs a solid-state method to prepare a sodium-ion battery cathode material with high capacity and high rate performance. The prepared sodium-ion battery cathode material has the chemical formula NaCu. 0.06 Zn 0.02 Mg 0.02 Ni 0.35 Fe 0.09 Al 0.01 Mn 0.3 Ti 0.15 O2.

[0077] The specific preparation steps include: weighing Na₂CO₃ (2wt% excess), CuO, ZnO, MgO, NiO, Fe₂O₃, Al₂O₃, MnO₂, and TiO₂ into a ball mill jar according to the stoichiometric ratio, adding an appropriate amount of zirconium dioxide grinding beads (bead-to-material ratio of 5:1), and then adding an appropriate amount of anhydrous ethanol and mixing evenly. The mixture is then ground at 600 rpm for 5 hours to obtain the precursor. The precursor is then treated in a crucible at 900°C in air for 15 hours to obtain a black powder. After grinding, the sodium-ion battery layered oxide cathode material NaCu of this invention is obtained. 0.06 Zn 0.02 Mg 0.02 Ni 0.35 Fe 0.09 Al 0.01 Mn 0.3 Ti 0.15 O2.

[0078] The XRD pattern of the sodium-ion cathode material prepared in this embodiment is as follows: Figure 1 As shown, comparison with the standard card reveals that its main phase is O3, space group R-3m, and no impurity phases are present. The scanning electron microscope (SEM) image of this layered oxide material is shown below. Figure 2 As shown, the layered oxide cathode material consists of single-crystal particles with a diameter of 1.5-3 μm, a smooth surface, no obvious residual alkali particles, and the presence of nano-sized aluminum oxide particles. The aberration-corrected scanning transmission electron microscope (AC-STEM) image of this layered oxide cathode material is shown below. Figure 3 As shown in the figure, the Fast Fourier Transform (FFT) graph indicates that it is a single crystal, and its TM layer spacing is... Figure 4 The STEM-EDS mapping diagram (Fig. a) and elemental content diagram (Fig. b) of this cathode material show that there is a concentration gradient of Zn on the surface.

[0079] The electrochemical performance of the sodium-ion battery layered oxide cathode material prepared in this embodiment was tested.

[0080] Half-cell assembly: Sodium-ion battery layered oxide cathode material was slurried with conductive carbon black (Super P) and vinylidene fluoride (PVDF) at a mass ratio of 80:10:10 in an N-methylpyrrolidone (NMP) solution and coated onto aluminum foil. The slurry was then cut into 10 mm diameter electrode sheets (with a loading of approximately 4 mg / cm³). 2 Using a sodium metal sheet as the negative electrode and a 1 mol / L solution of NaClO4 / polycarbonate (PC): ethylene carbonate (EC): dimethyl carbonate (DMC) (volume ratio 1:1:1) + 2% Vol of fluorinated ethylene carbonate (FEC) as the electrolyte, and employing a glass fiber diaphragm, a CR2032 coin cell half-cell was assembled in an argon glove box.

[0081] Charge / discharge testing: The charge / discharge voltage range for the coin cell batteries is 2.0-4.2V or 2.0-4.1V. Before conducting a 100-cycle test at 2.0-4.2V, the batteries were first charged and discharged three times at a lower current density of 15mA / g, followed by cycling at a current density of 150mA / g within the same voltage range. Before conducting a 1000-cycle test at 2.0-4.1V, the batteries were first charged and discharged three times at a lower current density of 15mA / g, followed by cycling at current densities of 450mA / g and 750mA / g within the same voltage range. Electrochemical performance tests were all conducted at room temperature, and the results are as follows: Figure 5-9 As shown.

[0082] Figure 5 The specific capacity-cycle curve of a sodium-ion half-cell assembled with the layered oxide cathode material prepared in Example 1 of the present invention during the first 100 cycles under 1C / 1C, 2-4.2V conditions. Figure 6 The specific capacity-cycle curve of a sodium-ion half-cell assembled with the layered oxide cathode material prepared in Example 1 of this invention during the first 1000 cycles under 3C / 3C, 2-4.1V conditions. Figure 7 The specific capacity-cycle curve of a sodium-ion half-cell assembled with the layered oxide cathode material prepared in Example 1 of this invention during the first 1000 cycles under 5C / 5C, 2-4.1V conditions. Figure 8 The specific capacity-voltage diagram of a sodium-ion half-cell assembled with the layered oxide cathode material prepared in Example 1 of this invention during the first 3 weeks of testing under 0.1C / 0.1C, 2-4.1V conditions; Figure 9 The rate performance of a sodium-ion half-cell assembled from the layered oxide cathode material prepared in Example 1 of this invention is shown in the figure, tested under conditions of 2-4.1V.

[0083] according to Figure 5-7 It can be seen that the discharge capacity decay of Example 1 is slower. Figure 8 It can be seen that the material exhibits good reversibility at the charging cutoff voltage of 4.1V. Figure 9 As can be seen, the material exhibits excellent rate performance, maintaining a specific capacity of 122.3 mAh / g at a current density of 10C (1.5 A / g). Therefore, the technical solution of this invention achieves high capacity retention in sodium-ion batteries at high voltages, and the application of the sodium-ion cathode material of this invention enables batteries to possess high energy density and long cycle life.

[0084] Example 2

[0085] This embodiment employs a solid-state method to prepare a sodium-ion battery cathode material with high capacity and high rate performance. The prepared sodium-ion battery cathode material has the chemical formula NaCu. 0.05 Zn 0.02 Mg0.005 Ni 0.35 Fe 0.125 Al 0.025 Mn 0.3 Ti 0.125 O2.

[0086] The specific steps include: weighing Na₂CO₃ (2wt% excess), CuO, ZnO, MgO, NiO, Fe₂O₃, Al₂O₃, MnO₂, and TiO₂ into a ball mill jar according to the stoichiometric ratio; adding an appropriate amount of zirconium dioxide grinding beads (bead-to-material ratio of 5:1); adding an appropriate amount of anhydrous ethanol; mixing evenly; and grinding at 600 rpm for 5 hours to obtain a precursor. The precursor is then treated in air at 900°C for 15 hours to obtain a black powder. After grinding, the sodium-ion battery layered oxide cathode material NaCu of this invention is obtained. 0.0 5Zn 0.02 Mg 0.005 Ni 0.35 Fe 0.125 Al 0.025 Mn 0.3 Ti 0.125 O2.

[0087] The XRD pattern of the sodium-ion cathode material prepared in this embodiment is as follows: Figure 1 As shown, by comparing with the standard card, it can be seen that its main phase is O3 phase, space group is R-3m, and no impurity phases exist.

[0088] Example 3

[0089] This embodiment employs a solid-state method to prepare a sodium-ion battery cathode material with high capacity and high rate performance. The prepared sodium-ion battery cathode material has the chemical formula NaCu. 0.05 Zn 0.025 Mg 0.01 Ni 0.35 Fe 0.12 Al 0.02 Mn 0.275 Ti 0.15 O2.

[0090] The specific steps include: weighing Na2CO3 (2wt% excess), CuO, ZnO, MgO, NiO, Fe2O3, Al2O3, MnO2, and TiO2 into a ball mill jar according to the stoichiometric ratio; adding an appropriate amount of zirconium dioxide grinding beads (bead-to-material ratio of 5:1); adding an appropriate amount of anhydrous ethanol and mixing evenly; and grinding at 600 rpm for 5 hours to obtain a precursor. The precursor is then treated at 900°C in air for 15 hours to obtain a black powder. After grinding, this becomes the layered oxide cathode material NaCu of the present invention. 0.05 Zn 0.025 Mg 0.01 Ni0.35 Fe 0.12 Al 0.02 Mn 0.275 Ti 0.15 O2.

[0091] The XRD pattern of the sodium-ion cathode material prepared in this embodiment is as follows: Figure 1 As shown, by comparing with the standard card, it can be seen that its main phase is O3 phase, space group is R-3m, and no impurity phases exist.

[0092] Example 4

[0093] This embodiment utilizes the sol-gel method to prepare a high-capacity, high-rate sodium-ion battery cathode material. The prepared sodium-ion battery cathode material has the chemical formula NaCu. 0.06 Zn 0.02 Mg 0.02 Ni 0.35 Fe 0.09 Al 0.01 Mn 0.3 Ti 0.15 O2.

[0094] The specific preparation steps include: weighing CH3COO Na (2wt% excess), Cu(CH3COO)2, Zn(NO3)2, Mg(NO3)2, Ni(CH3COO)2, Fe(NO3)2, Al(NO3)3, Mn(NO3)2, TiOSO4, and an appropriate amount of citric acid according to the stoichiometric ratio, and dissolving them in deionized water to form a mixed solution. The solution is heated and stirred in a constant-temperature oil bath for 4 hours, and the temperature is adjusted to 100℃ to evaporate and form a gel. The resulting gel is placed in a crucible and pretreated at 500℃ for 3 hours. The pretreated powder is then ground and placed in a crucible, sintered at 1000℃ in an air or oxygen atmosphere for 10 hours, cooled to room temperature, and ground under an inert atmosphere to obtain the layered oxide cathode material of this invention.

[0095] The precursor was treated in a crucible at 900°C for 15 hours in air atmosphere to obtain a black powder. After grinding, the sodium-ion battery layered oxide cathode material NaCu of this invention was obtained. 0.06 Zn 0.02 Mg 0.02 Ni 0.35 Fe 0.09 Al 0.01 Mn 0.3 Ti 0.1 5O2.

[0096] Example 5

[0097] This embodiment employs a co-precipitation-solid phase method to prepare a high-capacity, high-rate sodium-ion battery cathode material. The prepared sodium-ion battery cathode material has the chemical formula NaCu.0.06 Zn 0.02 Mg 0.02 Ni 0.35 Fe 0.09 Al 0.01 Mn 0.3 Ti 0.15 O2.

[0098] The specific preparation steps include: according to the molecular formula NaCu 0.06 Zn 0.02 Mg 0.02 Ni 0.35 Fe 0.09 Al 0.01 Mn 0.3 Ti 0.15 Prepare a deionized aqueous solution of NiSO4·6H2O, FeSO4·7H2O, and MnSO4·H2O sulfates (i.e., a transition metal solution) with a concentration of 2 mol / L using the stoichiometric ratio of O2. Prepare an alkaline solution using sodium hydroxide, ammonia, and deionized water, with a sodium hydroxide concentration of 4 mol / L and an ammonia concentration of 1 mol / L. Add an appropriate amount of deionized water to the reaction vessel and purge with nitrogen gas. Heat to 70°C and maintain the temperature while stirring at 1000 r / min. Then, simultaneously add the transition metal solution and the alkaline solution, maintaining the pH at approximately 11.5. After the reaction is complete, filter and wash the precipitate, and dry it at 120°C for 5 hours to obtain a Ni-Fe-Mn precursor with uniform elemental distribution.

[0099] Weigh out NaOH (2wt% excess), Ni-Fe-Mn precursor, CuO, ZnO, Al2O3, MgO, and TiO2 according to the stoichiometric ratio. Add an appropriate amount of zirconium dioxide grinding beads (bead-to-material ratio of 5:1), then add an appropriate amount of anhydrous ethanol and mix thoroughly. Grind at 600 rpm for 5 hours. Treat the ball-milled product at 900°C for 12 hours in an oxygen atmosphere to obtain a black powder. After grinding, this is the layered oxide cathode material NaCu of the present invention. 0.06 Zn 0.02 Mg 0.02 Ni 0.35 Fe 0.09 Al 0.01 Mn 0.3 Ti 0.15 O2.

[0100] Comparative Example

[0101] This comparative example uses a solid-state method to prepare NaNi. 0.35 Fe 0.3 Mn 0.35 O2.

[0102] The specific steps include: weighing Na₂CO₃ (2wt% excess), Fe₂O₃, and MnO₂ into a ball mill jar according to the stoichiometric ratio, adding an appropriate amount of zirconium dioxide grinding beads (bead-to-material ratio of 5:1), and then adding an appropriate amount of anhydrous ethanol and mixing evenly. The mixture is then ground at 600 rpm for 5 hours to obtain the precursor. The precursor is then treated in a crucible at 900°C in air atmosphere for 15 hours to obtain a black powder, which is then ground and set aside as the layered oxide cathode material NaNi of Comparative Example 1. 0.35 Fe 0.3 Mn 0.35 O2.

[0103] The XRD pattern of the Ni-Fe-Mn based sodium cathode material prepared in this comparative example is shown below. Figure 1 As shown, by comparing with the standard card, it can be seen that its main phase is O3 phase material, space group is R-3m, and there is a small amount of nickel oxide impurity.

[0104] The high-capacity, high-rate performance sodium-ion battery cathode material provided in this invention utilizes only elements with atomic numbers less than or equal to 30 for high-entropy design, avoiding the use of heavier elements. By controlling the Ti content and the selection of dopant element M, the migration of Fe during charging is suppressed. Simultaneously, the use of smaller amounts of Zn, Mg, and Al avoids the precipitation of other oxide impurities due to solid solubility. The rational use of nickel as a charge compensation element helps improve the electrochemical performance of the cathode at high cutoff voltages. The concentration gradient of zinc on the surface and the coating effect of aluminum oxide formed by the difference in solid solubility stabilize the material surface. By adjusting the bonding between the transition metal and oxygen in the sodium-ion layered oxide cathode material, a high-capacity, high-rate performance sodium-ion battery cathode material can be obtained.

[0105] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A sodium-ion cathode material with high capacity and high rate performance, characterized in that, The high-capacity, high-rate performance sodium-ion battery cathode material has the chemical formula Na. x Cu a Zn b Ni c Fe d Al e Mn f Ti g M h O 2±α Cu, Zn, Ni, Fe, Mn, and Ti are transition metal elements; Al is a light metal element with atomic number 13; M is an element with atomic number less than or equal to 20, and must contain at least Mg. The sodium-ion cathode material is a layered oxide material with space group R-3m and corresponding structure O3 phase; x, a, b, c, d, e, f, g, h and 2±α are the molar percentages of the corresponding elements, and each component in the chemical formula satisfies charge conservation and stoichiometric ratio conservation, that is, x+2×(a+b+c)+3×(d+e)+4×(f+g)+k×h=2×(2±α) and a+b+c+d+e+f+g+h=1, where k is the average chemical valence state of element M, and 0.9≤x≤1.03, 0<a<0.1, 0<b<0.05, 0.33<c≤0.4, 0.05<d<0.15, 0<e<0.03, 0.2≤f≤0.3, 0<g≤0.2, 0<h≤0.05, 0≤α≤0.05; The Zn element exhibits a concentration gradient distribution on the surface of the sodium-ion battery cathode material, and the surface of the sodium-ion battery cathode material also has an island-like coating structure of aluminum oxide.

2. The sodium-ion cathode material according to claim 1, characterized in that, The sodium-ion cathode material is used as the positive electrode active material in sodium-ion secondary batteries.

3. A method for preparing the sodium-ion cathode material according to claim 1 or 2, characterized in that, The preparation method is a solid-state method, including: According to the required stoichiometric ratio, excess 0%-10wt% of sodium source, the required stoichiometric amounts of copper source, zinc source, nickel source, iron source, aluminum source, manganese source, titanium source and M-containing precursor are mixed in proportion, anhydrous ethanol, isopropanol or acetone are added, and the mixture is ball-milled at 100-700 rpm for 1-12 hours to obtain powder. The obtained powder is placed in a crucible and sintered in an atmosphere of air or pure oxygen. It is calcined at 800-1100℃ for 1-20 hours, cooled to room temperature, and then ground to obtain a layered oxide cathode material for sodium-ion batteries, which is the sodium battery cathode material. The sodium source includes at least one of sodium hydroxide, sodium carbonate, sodium nitrate, sodium oxide, sodium peroxide, sodium acetate, and sodium oxalate. The copper source, zinc source, nickel source, iron source, aluminum source, manganese source, and titanium source respectively include at least one of the following: metal oxides, metal carbonates, metal nitrates, metal oxalates, metal acetates, metal sulfates, and metal hydroxides containing copper, zinc, nickel, iron, aluminum, manganese, and titanium. The precursor containing M includes at least one of the following: oxides, carbonates, nitrates, oxalates, acetates, sulfates, and hydroxides containing M; M is an element with an atomic number less than or equal to 20, and contains at least Mg.

4. A method for preparing the sodium-ion cathode material according to claim 1 or 2, characterized in that, The preparation method is a sol-gel method, including: According to the required stoichiometric ratio, an excess of 0%-10wt% sodium source, the required stoichiometric amounts of copper source, zinc source, nickel source, iron source, aluminum source, manganese source, titanium source, precursor containing M, and an appropriate amount of citric acid are dissolved in deionized water to form a mixed solution. The resulting mixed solution was evaporated at a constant temperature in an oil bath to form a gel; The obtained gel is placed in a crucible and pretreated at 300-600℃ for 1-20 hours. The powder obtained after pretreatment is then ground and placed in a crucible. It is then sintered at 800-1100℃ in an air or oxygen atmosphere for 1-20 hours. After cooling to room temperature, it is ground in an inert atmosphere to obtain a layered oxide cathode material for sodium-ion batteries, which is the sodium battery cathode material. The sodium source, copper source, zinc source, nickel source, iron source, aluminum source, manganese source, titanium source, and precursor containing M respectively include: soluble salts containing sodium, copper, zinc, nickel, iron, aluminum, manganese, titanium, and M. The soluble salt includes at least one of the following: nitrate, oxalate, acetate, or sulfate of the corresponding metal; M is an element with an atomic number less than or equal to 20, and contains at least Mg.

5. A method for preparing the sodium-ion cathode material according to claim 1 or 2, characterized in that, The preparation method is a coprecipitation-solid phase method, including: The Ni-Fe-Mn precursor was obtained by co-precipitation, specifically as follows: Na x Cu a Zn b Ni c Fe d Al e Mn f Ti g M h O 2±α A deionized aqueous solution of NiSO4·6H2O, FeSO4·7H2O, and MnSO4·H2O sulfates, i.e., a transition metal solution, was prepared according to the stoichiometric ratio. An alkaline solution was prepared using sodium hydroxide, ammonia, and deionized water. An appropriate amount of deionized water was added to the reaction vessel, and nitrogen gas was introduced. The mixture was heated and kept at a constant temperature. Then, while stirring, the transition metal solution and the alkaline solution were added dropwise, and the pH was maintained between 11.3 and 11.

8. After the reaction was completed, the precipitate was filtered, washed, and dried to obtain a Ni-Fe-Mn precursor with uniform elemental distribution. According to the required stoichiometric ratio, an excess of 0%-10wt% sodium source, the required stoichiometric amount of Ni-Fe-Mn precursor, copper source, zinc source, aluminum source, titanium source and M-containing precursor are mixed and ball-milled for 1-20 hours, and sintered at 800℃-1100℃ for 1-20 hours in air or oxygen atmosphere to obtain sodium-ion battery layered oxide cathode material, which is the sodium battery cathode material mentioned above. The sodium source includes one or more of sodium hydroxide, sodium carbonate, sodium nitrate, sodium oxide, sodium peroxide, and sodium oxalate. The copper source, zinc source, aluminum source, and titanium source each include at least one of the following: metal oxides, metal carbonates, metal nitrates, metal oxalates, metal acetates, metal sulfates, and metal hydroxides containing copper, zinc, aluminum, and titanium. The precursor containing M includes at least one of the following: oxides, carbonates, nitrates, oxalates, acetates, sulfates, and hydroxides containing M; M is an element with an atomic number less than or equal to 20, and contains at least Mg.

6. A sodium-ion secondary battery electrode material, characterized in that, The sodium-ion secondary battery electrode material includes: conductive additives, binders, and the high-capacity, high-rate performance sodium-ion positive electrode material as described in claim 1 or 2.

7. The sodium-ion secondary battery electrode material according to claim 6, characterized in that, The conductive additive includes at least one of the following: carbon black, acetylene black, graphite powder, carbon nanotubes, graphene, and nitrogen-doped carbon. The adhesive includes at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), sodium alginate, sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR).

8. A positive electrode sheet comprising the sodium-ion secondary battery electrode material as described in claim 6 or 7.

9. A sodium-ion secondary battery comprising the positive electrode sheet as described in claim 8.

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