Layered oxide positive electrode material, preparation method and sodium ion battery

Abstract

The invention discloses a layered oxide positive electrode material, a preparation method and a sodium ion battery, and the method comprises the following steps: S1, calcining by taking multi-element MOFs as a sacrificial precursor to obtain a high-entropy oxide; s2, mixing the high-entropy oxide with a sodium source to obtain a precursor; and S3, sintering the precursor to obtain the layered oxide positive electrode material. According to the method, multi-element MOFs are used as a sacrificial precursor to be calcined to form a high-entropy oxide containing various metal ions, ions can be migrated more uniformly without higher energy during mixed sintering of the high-entropy oxide and a sodium source, and the porous structure of the multi-element MOFs material is more beneficial to entry of the sodium source, so that the performance of the multi-element MOFs material is improved, and the service life of the multi-element MOFs material is prolonged. The problem of mixing uniformity of solid-phase reaction is effectively solved, and the effects of reducing the reaction temperature and reducing the energy consumption are achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and particularly relates to a layered oxide cathode material, a preparation method and a sodium ion battery. Background Art

[0002] At present, the positive active materials of sodium ion batteries are mainly divided into three categories: layered oxides, Prussian blue and polyanions. Prussian blue and polyanion-based positive active material materials are difficult to synthesize due to the inherent defects of the materials, and the material consistency is poor, making it difficult to be applied to sodium ion batteries. On the other hand, the preparation process of layered oxide-based active material materials is relatively simple and the preparation process is controllable, which is considered to be the most promising positive electrode material for sodium ion batteries.

[0003] At present, when using the solid phase method in the process of preparing the layered cathode material of sodium ion batteries, the raw materials are generally directly mixed and calcined at high temperature. The advantages of this method are simple operation, easy control, short process flow and low cost. However, due to the slow diffusion rate of solid phase reaction, a higher temperature and time are required to ensure the full reaction, resulting in large energy consumption. On the other hand, the uneven mixing of reactants leads to poor homogeneity of the synthesized samples.

[0004] During the charge and discharge process of the layered cathode material, due to the insertion and extraction of sodium ions with a larger radius complex phase transitions will occur, such as hexagonal O3, monoclinic O'3, hexagonal P3, monoclinic P'3, and even other highly destructive structures, which will accumulate cracks during long-term cycling, ultimately leading to battery capacity decay, short cycle life, poor rate performance and premature failure. Summary of the Invention

[0005] The main object of the present invention is to provide a layered oxide cathode material, a preparation method and a sodium ion battery, aiming to solve the technical problems of poor uniformity and cycling performance of existing sodium ion battery cathode materials.

[0006] To achieve the above object, the first aspect of the present invention proposes a preparation method of a layered oxide cathode material, including the following steps:

[0007] S1: Calcining with a multi-component MOF as a sacrificial precursor to obtain a high-entropy oxide;

[0008] S2: Mixing the high-entropy oxide with a sodium source to obtain a precursor;

[0009] S3: Sintering the precursor to obtain the layered oxide cathode material.

[0010] Further, before the step of calcining with a multi-component MOF as a sacrificial precursor to obtain a high-entropy oxide, it includes:

[0011] Disperse a preset metal salt solution into a liquid-phase solvent to prepare Solution A;

[0012] Disperse an organic ligand into a liquid-phase solvent to prepare Solution B;

[0013] Add Solution B to Solution A to form a mixed solution;

[0014] Transfer the obtained mixed solution to a high-pressure reactor and heat it in an oven for reaction;

[0015] Wash the product after the heat reaction with deionized water and ethanol repeatedly, filter by suction and vacuum dry in a vacuum drying oven to obtain the multi-component MOFs.

[0016] Furthermore, the metal elements are selected from five or more of Ni, Fe, Mn, Cu, Ca, Co, Zn, Ti, Zr, Mg, Al, and Nb

[0017] Furthermore, the liquid-phase solvent is selected from one or more of water, methanol, ethanol, ethylene glycol, propanol, tetrahydrofuran, and N,N-dimethylformamide

[0018] Furthermore, the organic ligand is selected from one of isophthalic acid, phthalic acid, terephthalic acid, trimesic acid, 1,2,4-benzenetricarboxylic acid, and 1,3,5-benzenetricarboxylic acid, benzimidazole, 2-methylimidazole, citric acid, sodium citrate, and oxalic acid.

[0019] Furthermore, the step of mixing the high-entropy oxide with a sodium source to obtain a precursor includes:

[0020] Mix the high-entropy oxide with the sodium source by ball milling to obtain the precursor, wherein the ball milling speed is 400 r / min to 600 r / min and the ball milling time is 2 h to 4 h.<{

[0021] Furthermore, the sodium source is one or more of sodium carbonate, sodium bicarbonate, sodium oxide, or sodium hydroxide.

[0022] Furthermore, the calcination temperature for calcining with the multi-component MOFs as a sacrificial precursor in S1 is 400 to 700 °C.

[0023] Furthermore, the sintering temperature for sintering the precursor in S3 is 800 to 1100 °C.

[0024] A layered oxide cathode material is proposed in the second aspect of the present invention, which is prepared by the preparation method of the layered oxide cathode material in any of the above embodiments.

[0025] Furthermore, the general formula of the layered oxide cathode material is Na a Ni x Fey Mn z M b O₂, where 0.67 ≤ a ≤ 1, 0.1 ≤ x ≤ 0.3, 0.1 ≤ y ≤ 0.4, 0.1 ≤ z ≤ 0.4, 0.1 ≤ b ≤ 0.3, and x + y + z + b = 1.

[0026] In the fourth aspect of the present invention, a sodium ion battery is proposed, including the layered oxide cathode material described in the above embodiments.

[0027] Beneficial effects:

[0028] For the layered oxide cathode material, preparation method and battery of the present invention, by calcining a multi-component MOF as a sacrificial precursor to obtain a high-entropy oxide, then mixing the high-entropy oxide with a sodium source to obtain a precursor, and sintering the precursor to obtain the layered oxide cathode material. On the one hand, the multi-component MOF itself is a metal-organic framework material composed of the coordination of multiple metal ions and organic ligands. Using the multi-component MOF as a sacrificial precursor and calcining it to form a high-entropy oxide containing multiple metal ions, the high-entropy oxide and the sodium source can make the ion migration more uniform without higher energy during the mixing and sintering process. On the other hand, for the prepared layered oxide cathode material, transition metal elements such as iron, nickel, manganese, etc. provide charge compensation during charge and discharge, and electrochemically inert elements such as Ca, Mg, etc. can stabilize the main structure, effectively inhibiting the phase change during the insertion and extraction of sodium ions, slowing down the generation of microcracks, effectively inhibiting the side reaction with the electrolyte during the cycling process, inhibiting the dissolution of transition metals, and improving the cycling stability. Description of the drawings

[0029] Figure 1 XRD pattern of the layered oxide cathode material prepared in Example 1 of the present invention;

[0030] Figure 2 XRD pattern of the layered oxide cathode material prepared in Comparative Example 4 of the present invention;

[0031] Figures 3-15 SEM images of the layered oxide cathode materials prepared in Examples 1 - 13 of the present invention;

[0032] Figures 16-19 SEM images of the layered oxide cathode materials prepared in Comparative Examples 1 - 4 of the present invention;

[0033] Figure 20 Element distribution map of the layered oxide cathode material prepared in Example 1;

[0034] Figure 21 Charge-discharge curves of the layered oxide cathode materials prepared in some examples and some comparative examples of the present invention at a current of 13 mA / g;

[0035] Figure 22 The charge-discharge cycle performance diagram (voltage range 2.0 - 4.0V) of the layered oxide cathode materials prepared in some embodiments and some comparative examples of the present invention at a current of 130 mA / g.

[0036] The realization, functional characteristics, and advantages of the object of the present invention will be further described in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Embodiments

[0037] It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0038] An embodiment of the present invention provides a method for preparing a layered oxide cathode material, including the following steps:

[0039] S1: Calcining a multi-component MOF as a sacrificial precursor to obtain a high-entropy oxide;

[0040] S2: Mixing the high-entropy oxide with a sodium source to obtain a precursor;

[0041] S3: Sintering the precursor to obtain the layered oxide cathode material.

[0042] By calcining a multi-component MOF as a sacrificial precursor to obtain a high-entropy oxide, then mixing the high-entropy oxide with a sodium source to obtain a precursor, and sintering the precursor to obtain the layered oxide cathode material. On the one hand, the multi-component MOF itself is a metal-organic framework material composed of the coordination of multiple metal ions and organic ligands. Using the multi-component MOF as a sacrificial precursor and calcining it to form a high-entropy oxide containing multiple metal ions. When the high-entropy oxide and the sodium source are mixed and sintered, the ions can migrate more uniformly without requiring higher energy. The MOF-derived metal oxides can easily form various porous or hollow structures with adjustable structures and compositions. MOF is the abbreviation of metal-organic framework compound, which is a class of crystalline porous materials with a periodic network structure formed by the self-assembly connection of inorganic metal centers (metal ions or metal clusters) and bridging organic ligands. Since a part of the porous structure of the multi-component MOF material itself is still retained after calcination, it is more conducive to the entry of the sodium source, effectively solving the problem of the mixing uniformity of the solid-phase reaction, achieving the effect of reducing the reaction temperature and reducing energy consumption; on the other hand, during charge and discharge of the prepared layered oxide cathode material, transition metal elements such as iron, nickel, and manganese provide charge compensation, and electrochemically inert elements such as Ca and Mg can stabilize the main structure, effectively inhibiting the phase change during the insertion and extraction of sodium ions, slowing down the generation of microcracks, effectively inhibiting the side reaction with the electrolyte during the cycle process, inhibiting the dissolution of transition metals, and improving the cycle stability.

[0043] In one embodiment, before the step of calcining the multi-component MOFs as a sacrificial precursor to obtain a high-entropy oxide, the following steps are included:

[0044] Disperse a preset metal salt solution into a liquid-phase solvent to prepare solution A;

[0045] Disperse an organic ligand into a liquid-phase solvent to prepare solution B;

[0046] Add solution B to solution A to form a mixed solution, and stir evenly at room temperature;

[0047] Transfer the obtained mixed solution to a high-pressure reactor, and heat and react in an oven; wherein, the inner lining of the high-pressure reactor is a polytetrafluoroethylene inner lining;

[0048] Wash the product after the heat reaction with deionized water and ethanol repeatedly, filter by suction and vacuum dry in a vacuum drying oven to obtain the multi-component MOFs.

[0049] In one embodiment, the liquid-phase solvent is selected from one or more of water, methanol, ethanol, ethylene glycol, propanol, tetrahydrofuran, and N,N-dimethylformamide

[0050] In one embodiment, the organic ligand is selected from one of isophthalic acid, phthalic acid, terephthalic acid, trimesic acid, 1,2,4-benzenetricarboxylic acid, and 1,3,5-benzenetricarboxylic acid, benzimidazole, 2-methylimidazole, citric acid, sodium citrate, and oxalic acid

[0051] In one embodiment, the multi-component MOFs are NiFeMnM-based multi-component MOFs, wherein M is a combination of at least five divalent or trivalent transition metal elements.

[0052] In the above embodiment, the metal elements of the metal salt solution include five or more of Ni, Fe, Mn, Cu, Ca, Co, Zn, Ti, Zr, Mg, Al, and Nb. Ni, Fe, and Mn, as the main elements in the battery cathode material, can provide a relatively high energy density and good stability at the same time. The multi-component MOFs can be multi-component Prussian blue analogs containing five metal elements or more than five metal elements, and high-entropy oxides can be formed by calcination.

[0053] In one embodiment, the step of mixing the high-entropy oxide with a sodium source to obtain a precursor includes: mixing the high-entropy oxide and the sodium source by ball milling to obtain the precursor, wherein the ball milling speed is 400 r / min to 600 r / min, and the ball milling time is 2 h to 4 h. Ball milling the calcined high-entropy oxide and the sodium source can efficiently disperse and remix the high-entropy oxide and the sodium source, ensuring uniform distribution of each component in the material. The ball milling speed can be 400 r / min, 450 r / min, 500 r / min, 550 r / min or 600 r / min, etc., but is not limited to the listed values, and other unlisted values within this range are equally applicable. For example, the ball milling time can be 2 h, 2.2 h, 2.4 h, 2.6 h, 2.8 h, 3 h, 3.2 h, 3.4 h, 3.6 h, 3.8 h or 4 h, etc., but is not limited to the listed values, and other unlisted values within this range are equally applicable. When the ball milling speed is lower than 400 r / min and the ball milling time is short, the grinding efficiency is low and it is easy to be insufficiently ground; when the ball milling speed is higher than 600 r / min, the contact probability between the zirconia balls in the ball mill and the high-entropy oxide or the sodium source is smaller. If the ball milling time is long, the energy consumption is high. Therefore, appropriate ball milling speed and ball milling time can increase the friction between the zirconia balls and the material, and effective grinding and sufficient mixing can be achieved between the high-entropy oxide and the sodium source.

[0054] In one embodiment, the sodium source is one or more of sodium carbonate, sodium bicarbonate, sodium oxide or sodium hydroxide. Sodium carbonate, sodium bicarbonate, sodium oxide or sodium hydroxide can all provide a sodium source for the cathode material to serve as embeddable ions for a sodium-ion battery.

[0055] In one embodiment, the calcination temperature is 400 to 700 °C. For example, it can be 400 °C, 450 °C, 500 °C, 600 °C, 650 °C or 700 °C, etc., but is not limited to the listed values, and other unlisted values within this range are equally applicable. The setting of the calcination temperature is sufficient for the decomposition of the multi-component MOFs to form high-entropy oxides.

[0056] In one embodiment, the sintering temperature is 800 to 1100 °C. For example, it can be 800 °C, 850 °C, 900 °C, 950 °C, 1000 °C, 1050 °C or 1100 °C, etc., but is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0057] The second aspect of the present invention provides a layered oxide cathode material prepared by the preparation method of the layered oxide cathode material in any of the above embodiments.

[0058] In one embodiment, the general formula of the layered oxide cathode material is Na a Ni x Fey Mn z M b O₂, where 0.67 ≤ a ≤ 1, 0.1 ≤ x ≤ 0.3, 0.1 ≤ y ≤ 0.4, 0.1 ≤ z ≤ 0.4, 0.1 ≤ b ≤ 0.3, and x + y + z + b = 1. Here, 0.67 ≤ a ≤ 1. For example, it can be 0.67, 0.7, 0.8, 0.9, 1, etc., but not limited to the listed values, and other unlisted values within this range are equally applicable; 0.1 ≤ x ≤ 0.3. For example, it can be 0.1, 0.15, 0.2, etc., but not limited to the listed values, and other unlisted values within this range are equally applicable; 0.01 ≤ y ≤ 0.4. For example, it can be 0.01, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, etc., but not limited to the listed values, and other unlisted values within this range are equally applicable; 0.1 ≤ z ≤ 0.4. For example, it can be 0.01, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, etc., but not limited to the listed values, and other unlisted values within this range are equally applicable; 0.1 ≤ b ≤ 0.3. For example, it can be 0.1, 0.2, 0.25, 0.3, etc., but not limited to the listed values, and other unlisted values within this range are equally applicable.

[0059] The fourth aspect of the present invention proposes a sodium - ion battery, including the layered oxide cathode material described in the above - mentioned embodiments.

[0060] The following uses some specific embodiments to illustrate the preparation process and performance of the present invention.

[0061] Example 1

[0062] Dissolve Ni(NO₃)₂·6H₂O, Fe(NO₃)₃·9H₂O, Mn(NO₃)₂·4H₂O, Cu(NO₃)₂·3H₂O, Zn(NO₃)₂·6H₂O in deionized water to obtain a clear solution A, dissolve citric acid in deionized water to obtain a clear solution B, add solution B to solution A to form a mixed solution, stir evenly at room temperature, transfer the obtained solution to a stainless - steel autoclave with a polytetrafluoroethylene liner, and heat - react in an oven; wash repeatedly with deionized water and ethanol, filter by suction, and vacuum - dry in a vacuum drying oven to obtain (Ni₀.₂Mn₀.₃Cu₀.₁Zn₀.₁Fe₀.₁)₃[Fe 0.3 (CN)₆]₂, which will be abbreviated as M - MOFs hereafter, and M is the metal source.

[0063] S1: Calcinate NiFeMnCuZn-MOFs in an air atmosphere at 500 °C for 2 h with a heating rate of 3 °C / min, and then cool it naturally to obtain a metal oxide, where the molar ratio of each metal element is Ni:Fe:Mn:Cu:Zn = 0.2:0.3:0.3:0.1:0.1;

[0064] S2: Use Na2CO3 as the sodium source and ball-mill it with the above high-entropy metal oxide to mix evenly to obtain a precursor, and the ball-milling conditions are ball-milling at a speed of 550 r / min for 2 h;

[0065] S3: Sinter the precursor obtained in S2 at 900 °C in an air atmosphere for 15 h, cool it naturally to room temperature, then crush it by air flow and pass through a 300-mesh sieve to obtain the NaNi 0.2 Fe 0.3 Mn 0.3 Cu 0.1 Zn 0.1 O2 layered oxide cathode material.

[0066] Example 2

[0067] This example has the same remaining parameters as Example 1, except that the metal salts used are nickel nitrate, iron nitrate, manganese nitrate, magnesium nitrate, zirconium nitrate, the liquid-phase solvent is ethanol, the organic ligand is isophthalic acid, and the obtained multi-component MOFs are NiFeMnZrMg-MOFs, and the NaNi 0.2 Fe 0.3 Mn 0.3 Zr 0.1 Mg 0.1 O2 layered oxide cathode material.

[0068] Example 3

[0069] This example has the same remaining parameters as Example 1, except that the metal salts used are nickel nitrate, iron nitrate, manganese nitrate, titanium nitrate, cobalt nitrate, the liquid-phase solvent is methanol, the organic ligand is phthalic acid, and the obtained multi-component MOFs are NiFeMnTiCo-MOFs, and the NaNi 0.2 Fe 0.32 Mn 0.33 Ti 0.05 Co 0.1 O2 layered oxide cathode material. [[ID=5...]]

[0070] Example 4

[0071] This example has the same remaining parameters as Example 1, except that the multi-metal salts used are nickel nitrate, iron nitrate, manganese nitrate, calcium carbonate, aluminum nitrate, the liquid-phase solvent is ethylene glycol, the organic ligand is terephthalic acid, and the obtained multi-component MOFs are NiFeMnCaAl-MOFs, and the NaNi0.2 Fe 0.32 Mn 0.33 Ca 0.05 Al 0.1 O₂ layered oxide cathode material.

[0072] Example 5

[0073] This example has the same remaining parameters as Example 1, except that the multi-metal salt used is nickel nitrate, iron nitrate, manganese nitrate, niobium oxalate, zinc nitrate, and magnesium nitrate, the liquid-phase solvent is propanol, the organic ligand is trimesic acid, and the obtained multi-metal MOFs are NiFeMnCaAl-MOFs. After calcination, metal oxides are obtained. Among them, the molar stoichiometric ratio of each metal element is Ni:Fe:Mn:Nb:Zn:Mg = 0.2:0.25:0.25:0.1:0.1:0.1, and finally NaNi 0.2 Fe 0.25 Mn 0.25 Nb 0.1 Zn 0.1 Mg 0. ₁O₂ layered oxide cathode material.

[0074] Example 6

[0075] This example has the same remaining parameters as Example 1, except that the liquid-phase solvent is tetrahydrofuran, the organic ligand is 1,2,4-benzenetricarboxylic acid, and NaHCO₃ is used as the sodium source and ball-milled with the above high-entropy metal oxide to obtain a precursor. The ball-milling conditions are a rotation speed of 400 r / min and a ball-milling time of 4 h, and NaNi 0.2 Fe 0.3 Mn 0.3 Cu 0.1 Zn 0.1 O₂ layered oxide cathode material.

[0076] Example 7

[0077] This example has the same remaining parameters as Example 1, except that the liquid-phase solvent is N,N-dimethylformamide, the organic ligand is 1,3,5-benzenetricarboxylic acid, and NaOH is used as the sodium source and ball-milled with the above high-entropy metal oxide to obtain a precursor. The ball-milling conditions are a rotation speed of 600 r / min and a ball-milling time of 2 h, and NaNi 0.2 Fe 0.3 Mn 0.3 Cu 0.1 Zn 0.1 O₂ layered oxide cathode material.

[0078] Example 8

[0079] This example has the same remaining parameters as Example 1, except that the liquid-phase solvent is a mixed solution of ethanol and water, the organic ligand is benzimidazole, the calcination temperature in S1 is 400 °C for 5 h, and Na2O is used as the sodium source and ball-milled and mixed evenly with the above high-entropy metal oxide to obtain a precursor, obtaining NaNi 0.2 Fe 0.3 Mn 0.3 Cu 0.1 Zn 0.1 O2 layered oxide cathode material.

[0080] Example 9

[0081] This example has the same remaining parameters as Example 1, except that the liquid-phase solvent is a mixed solution of methanol and water, the organic ligand is 2-methylimidazole, the calcination temperature in S1 is 700 °C for 2 h, and the sintering temperature in S3 is 800 °C for 24 h, obtaining NaNi 0.2 Fe 0.3 Mn 0.3 Cu 0.1 Zn 0.1 O2 layered oxide cathode material.

[0082] Example 10

[0083] This example has the same remaining parameters as Example 1, except that the liquid-phase solvent is a mixed solution of ethylene glycol and methanol, the organic ligand is citric acid, and the sintering temperature in S3 is 1100 °C for 15 h, obtaining NaNi 0.2 Fe 0.3 Mn 0.3 Cu 0.1 Zn 0.1 O2 layered oxide cathode material.

[0084] Example 11

[0085] This example has the same remaining parameters as Example 1, except that the liquid-phase solvent is a mixed solution of propanol and tetrahydrofuran, the organic ligand is sodium citrate, and the used multi-component MOFs are NiFeMnCaAl-MOFs, obtaining Na 0.67 Ni 0.1 Fe 0.4 Mn 0. 4Ca 0.05 Al 0.05 O2 layered oxide cathode material.

[0086] Example 12

[0087] This example has the same remaining parameters as Example 1, except that the liquid-phase solvent is tetrahydrofuran and N,N-dimethylformamide, the organic ligand is oxalic acid, and the multi-component MOFs used are NiFeMnCaAl-MOFs, obtaining Na 0.67 Ni 0.3 Fe 0.1 Mn 0. 3Ca 0.05 Al 0.25 O2 layered oxide cathode material.

[0088] Example 13

[0089] This example has the same remaining parameters as Example 1, except that the multi-component MOFs used are NiFeMnCaAl-MOFs, obtaining Na 0.67 Ni 0.3 Fe 0.3 Mn 0.1 Ca 0.05 Al 0.25 O2 layered oxide cathode material.

[0090] Comparative Example 1

[0091] Directly weigh NiO, Fe2O3, MnO2, CuO, ZnO, Na2CO3 according to the molar stoichiometric ratio of each metal element as Ni:Fe:Mn:Cu:Zn:Na = 0.2:0.3:0.3:0.1:0.1:1.03, and ball-mill and mix evenly at a speed of 550 r / min for 2 h. Sinter the mixture at 1000 °C in an air atmosphere for 12 h, cool it naturally to room temperature, then crush it and pass through a 300-mesh sieve to obtain NaNi 0.2 Fe 0.3 Mn 0.3 Cu 0.1 Zn 0.1 O2 sodium-ion layered oxide cathode material.

[0092] Comparative Example 2

[0093] This comparative example is basically the same as Comparative Example 1, except that NiO, Fe2O3, MnO2, CuO, ZnO, Na2CO3 are replaced with NiO, Fe2O3, MnO2, CuO, MgO, obtaining NaNi 0.2 Fe 0.3 Mn 0.3 Cu 0.1 Mg 0.1 O2 sodium-ion layered oxide cathode material.

[0094] Comparative Example 3

[0095] This comparative example is basically the same as Comparative Example 1, except that NiO, Fe2O3, MnO2, CuO, ZnO, and Na2CO3 are replaced with NiO, Fe2O3, MnO2, Nb2O5, ZnO, and MgO to obtain NaNi 0.2 Fe 0.25 Mn 0.25 Nb 0.1 Zn 0.1 Mg 0.1 O2 sodium-ion layered oxide cathode material.

[0096] Comparative Example 4

[0097] S1: Calcinate the Ni / Fe / Mn / Cu / Zn Prussian blue analogue at 500 °C in an air atmosphere for 2 h with a heating rate of 3 °C / min and cool it naturally to obtain a metal oxide, where the molar stoichiometric ratio of each metal element is Ni:Fe:Mn:Cu:Zn = 0.2:0.3:0.3:0.1:0.1;

[0098] S2: Use Na2CO3 as the sodium source and ball-mill it with the above high-entropy metal oxide to obtain a precursor uniformly. The ball-milling conditions are a rotation speed of 550 r / min and a ball-milling time of 2 h;

[0099] S3: Sinter the precursor obtained in S2 at 700 °C in an air atmosphere for 15 h, cool it naturally to room temperature, and then crush it by air flow and pass through a 300-mesh sieve to obtain NaNi 0.2 Fe 0.3 Mn 0.3 Cu 0.1 Zn 0.1 O2 layered oxide cathode material.

[0100] This comparative example is basically the same as Example 1, except that the sintering temperature in S3 is 700 °C.

[0101] Please refer to Figures 21-22 , and test the capacity and cycle stability of the cathode materials prepared in Examples 1-10 and Comparative Examples 1-3. The test results are shown in the following table.

[0102] Test method and test conditions: The synthesized cathode material, binder (polyvinylidene fluoride), and conductive agent (acetylene black) are mixed and ground evenly according to a mass ratio of 90:5:5. Then, an appropriate amount of N-methylpyrrolidone (NMP) is added as a solvent, and they are evenly mixed into a viscous black slurry, which is then evenly scraped onto an aluminum foil current collector. The coated electrode sheet is dried in a vacuum oven at 110 °C, and then the dried electrode sheet is roll-pressed and then dried in a vacuum oven at 120 °C for 12 h to make an electrode sheet. The electrode sheet is punched and weighed, and the battery is assembled in a glove box. Among them, the electrolyte used for assembling the battery is an electrolyte composed of diethyl carbonate (DEC) and ethylene carbonate (EC) solvents containing sodium perchlorate (NaClO4) sodium salt. The sodium sheet is used as the counter electrode. The assembled battery is subjected to electrochemical performance testing. The test temperature is kept constant at 25 °C, and constant current charge and discharge testing are carried out in the voltage range of 2.0 - 4.0 V, and the nominal specific capacity is 130 mAh / g.

[0103]

[0104]

[0105] It can be proved from Examples 1 - 5 and Figure 1 that in the multi-component Prussian blue analogues containing any five or more divalent or trivalent transition metal element combinations of nickel, iron, manganese, and Ca, Cu, Zn, W, Nb, Mo, Al, Mg, the high-entropy oxide obtained by calcination can be mixed and sintered with a sodium source to obtain a layered oxide cathode material.

[0106] It can be seen from Comparative Examples 1 - 3 and the above-mentioned examples that the multi-component MOFs are synthesized by the co-precipitation method or the solvothermal method, etc., and the process is relatively simple. During the synthesis process, the introduced various metal ions and organic ligands are fully coordinated and connected during the reaction, and a stable framework structure can be formed. Mixing at the atomic level in the liquid phase to form multi-component MOFs has a better effect than directly mixing and calcining the raw materials in the existing solid-phase method. For example, in Comparative Example 1, directly calcining various metal oxides leads to uneven reactions and more impurities, as shown in ( Figure 2 ).

[0107] Referring to the above table and Figures 3-12 it can be seen that comparing the SEM images ([[]] Figures 16-19 [[]]) of the sodium ion layered oxide cathode materials prepared in Examples 1 - 10 with the cathode materials synthesized in Comparative Examples 1 - 4 shows that after the high-entropy oxide synthesized with multi-component MOFs as the sacrificial precursor is ball-milled and mixed with the sodium source, the required calcination temperature is lower, and the layered oxide cathode material obtained by sintering treatment has larger particles and a smaller specific surface area, reducing the degree of side reactions with the electrolyte, which is beneficial to the electrochemical performance; in Comparative Example Figures 16-18 the particles are severely agglomerated, while Figures 3-16 ​​The particle agglomeration degree of the examples is lower, and the batches and processing of the materials are more stable. Comparative examples Figures 16-18 There are more fine powders on the material surface, while Figures 3-16 the surface of the examples is cleaner, indicating that the particles can grow sufficiently at a relatively low temperature; Figure 20 The elemental distribution maps can prove that various metal elements in the sodium-ion layered oxide cathode material synthesized in Example 1 are very evenly distributed, which can reduce the local expansion and local contraction during the cyclic charge and discharge of the battery, thereby prolonging the cycle life of the battery.

[0108] It can be proved from the above data that the cathode materials obtained by direct mixing and calcination in Comparative Examples 1-3 have lower discharge specific capacity and cycle retention rate than those in Examples 1-10. This shows that direct mixing and calcination are prone to uneven reaction, slow diffusion rate, and poor homogeneity, resulting in poor cycle stability and capacity retention ability of the cathode material and relatively low energy density. And Comparative Example 4 is also obtained by mixing the calcined polyanion Prussian blue analogue with the sodium source. Compared with Comparative Examples 1-3, its battery capacity and cycle performance are better, but due to the sintering temperature being lower than that in Examples 1-10, it is difficult to react evenly, resulting in poor electrochemical performance. Verified by Figures 1-2 the comparison of the XRD patterns of Example 1 and Comparative Example 4 in Figure 16 and verified by Figure 2 When the sintering temperature is low, it is easy to form impurity phases. See the impurity peaks around 20 degrees, 37 degrees, and 42 degrees in

[0109] Verified by the comparison between Example 8 and Comparative Example 1, the layered oxide cathode material synthesized by using the preparation method of the present invention with a lower calcination temperature and a shorter calcination time also has good battery capacity and capacity retention rate. Therefore, it has the effect of reducing the reaction temperature and energy consumption.

[0110] It can be seen from Examples 1, 6-8 that sodium bicarbonate, sodium carbonate, sodium hydroxide, and sodium oxide can all provide sodium sources for the cathode material and can all be removed as gases after calcination without doping with other impurity elements.

[0111] The above are only the preferred embodiments of the present invention, and do not limit the patent scope of the present invention accordingly. Any equivalent structural or equivalent process transformation made by using the content of the specification and drawings of the present invention, or directly or indirectly applied to other related technical fields, shall be included in the patent protection scope of the present invention by the same token.

Claims

1. A method for preparing a layered oxide cathode material, characterized in that, Including the following steps: S1: Calcining a multi-component MOF as a sacrificial precursor to obtain a high-entropy oxide S2: Mixing the high-entropy oxide with a sodium source to obtain a precursor; S3: Sintering the precursor to obtain the layered oxide cathode material.

2. The preparation method of the layered oxide cathode material according to claim 1, wherein Before the step of calcining the multi-component MOF as a sacrificial precursor to obtain a high-entropy oxide, it includes: Dispersing a preset metal salt solution into a liquid-phase solvent to prepare solution A; Dispersing an organic ligand into a liquid-phase solvent to prepare solution B; Adding solution B to solution A to form a mixed solution; Transferring the obtained mixed solution to a high-pressure reactor and heating and reacting in an oven; Washing the product after the heating reaction repeatedly with deionized water and ethanol, filtering by suction and drying in a vacuum drying oven to obtain the multi-component MOF.

3. The preparation method of the layered oxide cathode material according to claim 2, characterized in that, The metal elements of the metal salt solution include at least five of Ni, Fe, Mn, Cu, Ca, Co, Zn, Ti, Zr, Mg, Al, and Nb.

4. The preparation method of the layered oxide cathode material according to claim 1, wherein, The step of mixing the high-entropy oxide with a sodium source to obtain a precursor includes: Mixing the high-entropy oxide and the sodium source by ball milling to obtain the precursor, wherein the ball milling speed is 400 r / min to 600 r / min and the ball milling time is 2 h to 4 h.

5. The preparation method of the layered oxide cathode material according to claim 1, characterized in that The sodium source is one or more of sodium carbonate, sodium bicarbonate, sodium oxide, or sodium hydroxide.

6. The preparation method of the layered oxide cathode material according to claim 1, wherein, The calcination temperature for calcining the multi-component MOF as a sacrificial precursor in S1 is 400 to 700 °C.

7. The preparation method of the layered oxide cathode material according to claim 1, wherein, The sintering temperature for sintering the precursor in S3 is 800 to 1100 °C.

8. A layered oxide cathode material, characterized in that, Prepared by the preparation method of the layered oxide cathode material according to any one of claims 1-7.

9. The layered oxide cathode material according to claim 8, wherein The general formula of the layered oxide cathode material is Na a Ni x Fe y Mn z M b O2, where 0.67 ≤ a ≤ 1, 0.1 ≤ x ≤ 0.3, 0.1 ≤ y ≤ 0.4, 0.1 ≤ z ≤ 0.4, 0.1 ≤ b ≤ 0.3, and x + y + z + b = 1.

10. A sodium-ion battery, characterized in that, Including the layered oxide cathode material according to any one of claims 8-9.

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