MOF-coated layered oxide positive electrode material, preparation method thereof and sodium ion battery

Abstract

The invention relates to the technical field of sodium ion batteries, in particular to an MOF-coated layered oxide positive electrode material, a preparation method thereof and a sodium ion battery. The preparation method comprises the following steps: ball-milling and mixing a metal source and a sodium source, and calcining to obtain a layered oxide positive electrode material; the preparation method comprises the following steps: adding Mn salt or Al salt and 2, 5-dihydroxy terephthalic acid into a mixed solvent composed of dimethyl amide, ethanol and deionized water, stirring, and reacting to obtain an MOF material; and mixing the layered oxide positive electrode material and the MOF material, and carrying out heat treatment to obtain the MOF-coated layered oxide positive electrode material. The MOF serving as a coating layer material has a large-aperture structure, a diffusion channel is provided for sodium ion transmission, and the migration rate of sodium ions is increased; mn-MOF or Al-MOF is used as a coating layer material, so that the surface oxygen defect concentration of the layered oxide positive electrode material can be adjusted, the reversibility of oxidation reduction of oxygen anions can be improved, and the coulombic efficiency and the cycling stability of the battery during charging and discharging under a high-voltage condition can be further improved.

Description

Technical Field

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

[0002] In recent years, with the booming development of electric vehicles and portable electronic devices, the demand for advanced energy storage systems with high energy density and safety has been increasing day by day. Lithium-ion batteries are widely used due to their advantages such as high energy density, high working voltage, and good cycle stability. However, due to the scarcity of lithium resources, uneven global distribution, and high mining costs, it is difficult for lithium-ion batteries to meet the growing application requirements. Compared with lithium, the content of sodium resources in the earth's crust is more than a thousand times that of lithium resources, and they are evenly distributed. At the same time, as a battery with high energy density, long cycle life, and environmental friendliness, sodium-ion batteries have attracted more and more attention from the scientific research community and the industrial community. The cathode materials of sodium-ion batteries mainly include layered oxides, Prussian compounds, and polyanion types. Among them, layered oxides have high energy density and simple preparation processes, but slightly poor stability and medium cycle life; Prussian compounds have low cost and high rate performance, but poor cycle life and low actual energy density; polyanion types have stable structures and outstanding cycle life, but low energy density and poor rate performance. In sodium-ion batteries, the cathode material is one of the key factors determining the battery performance. Layered oxides are considered ideal cathode materials for sodium-ion batteries due to their high ionic conductivity, reversible capacity, and good structural stability. However, in practical applications, there are still some problems with layered oxide cathode materials, such as phase transformation, gas generation, volume expansion, and material peeling during high-voltage charge-discharge cycling, which affect the stability and cycle performance of the battery.

[0003] Therefore, the existing technology still needs to be improved and developed. Summary of the Invention

[0004] In view of the above deficiencies of the prior art, the purpose of the present invention is to provide a layered oxide cathode material coated with MOF, a preparation method thereof, and a sodium-ion battery, aiming to solve the problem that the layered oxide cathode material of the existing sodium-ion battery cannot balance excellent rate performance, high Coulomb efficiency, and cycle stability during charge and discharge under high-voltage conditions.

[0005] The technical solution of the present invention is as follows:

[0006] In the first aspect of the present invention, a preparation method of a layered oxide cathode material coated with MOF is provided, which includes the following steps:

[0007] (1) Ball-mill and mix a metal source and a sodium source, then calcine, and after cooling, obtain a layered oxide cathode material;

[0008] (2) Add Mn salt or Al salt and 2,5-dihydroxyterephthalic acid into a mixed solvent composed of dimethylformamide, ethanol and deionized water, stir, then transfer to a reaction kettle for reaction, and purify the resulting suspension to obtain the MOF material;

[0009] (3) Mix the layered oxide cathode material obtained in step (1) and the MOF material obtained in step (2), and after heat treatment, obtain the MOF-coated layered oxide cathode material.

[0010] Optionally, in step (1), the sodium source is sodium carbonate or sodium hydroxide; the metal source includes a TM source and manganese dioxide, and the TM source is at least one of hydroxides of Li, oxides of Mg, oxides of Al, oxides of K, oxides of Ca, oxides of Cu, oxides of Sn, oxides of Y, oxides of Nb, oxides of Ni, oxides of Fe, oxides of Zn, oxides of Ti, oxides of Co.

[0011] Optionally, in step (1), the ball milling speed is 200 - 600 r / min, and the ball milling time is 2 - 10 h; the calcination temperature is 600 - 1000 °C, and the calcination time is 12 - 24 h.

[0012] Optionally, in step (1), the chemical formula of the layered oxide cathode material is Na x TM y Mn 1-y O2, where 0.5 ≤ x ≤ 1.1, 0 ≤ y ≤ 0.7, and TM is at least one of Li, Mg, Al, K, Ca, Cu, Sn, Y, Nb, Ni, Fe, Zn, Ti, Co.

[0013] Optionally, in step (2), the Mn salt is manganese chloride tetrahydrate, and the Al salt is aluminum chloride hexahydrate.

[0014] Optionally, in step (2), the volume ratio of dimethylformamide, ethanol and deionized water in the mixed solvent is 15 - 30:1:1.

[0015] Optionally, in step (2), the reaction temperature of the reaction kettle is 50 - 150 °C, and the reaction time is 5 - 20 h.

[0016] Optionally, in step (3), the mass ratio of the layered oxide cathode material to the MOF material is 1:0.005 - 0.1, the heat treatment temperature is 300 - 600 °C, and the heat treatment time is 3 - 6 h.

[0017] In the second aspect of the present invention, a layered oxide cathode material coated with MOF is provided, which is prepared by the method described in the present invention.

[0018] In the third aspect of the present invention, a sodium-ion battery is provided, including a positive electrode sheet, wherein the positive electrode sheet includes the layered oxide cathode material coated with MOF as described in the present invention.

[0019] Beneficial effects:

[0020] (1) As a coating layer material, MOF has a large pore diameter structure, providing a diffusion channel for the transport of sodium ions and enhancing the migration rate of sodium ions.

[0021] (2) Mn-MOF or Al-MOF as a coating layer material can adjust the surface oxygen defect concentration of the layered oxide cathode material, which is beneficial to improving the reversibility of oxygen anion redox, and further improving the rate performance, Coulomb efficiency and cycle stability of the battery during charge and discharge under high voltage conditions.

[0022] (3) The operation of the present invention is simple and the design is novel, providing a new idea for the coating method. Description of the drawings

[0023] Figure 1 XRD pattern of the Na 0.8 Li 0.2 Mn 0.8 O2 layered oxide cathode material prepared in Example 1;

[0024] Figure 2 XRD pattern of the Na 0.8 Mg 0.25 Mn 0.75 O2 layered oxide cathode material prepared in Example 2;

[0025] Figure 3 SEM image of the Na 0.8 Li 0.2 Mn 0.8 O2 layered oxide cathode material coated with Al-MOF prepared in Example 3;

[0026] Figure 4 SEM image of the Na 0.8 Mg 0.25 Mn 0.75 O2 layered oxide cathode material coated with Al-MOF prepared in Example 4;

[0027] Figure 5 For the galvanostatic intermittent titration method (GITT) of the positive electrode test of the sodium-ion battery prepared in Application Example 1 and Comparative Example 1 and the corresponding Na+ Diffusion coefficient diagram;

[0028] Figure 6 It is a comparison diagram of the cycling performance of the sodium-ion batteries of Application Example 1 and Comparative Example 1;

[0029] Figure 7 It is a comparison diagram of the rate performance of the sodium-ion batteries of Application Example 1 and Comparative Example 1;

[0030] Figure 8 It is a cyclic voltammetry (CV) diagram of the positive electrode of the sodium-ion battery prepared in Application Example 2 and Comparative Example 2;

[0031] Figure 9 It is a comparison diagram of the cycling performance of the sodium-ion batteries of Application Example 2 and Comparative Example 2;

[0032] Figure 10 It is a comparison diagram of the rate performance of the sodium-ion batteries of Application Example 2 and Comparative Example 2. Detailed implementation manners

[0033] The present invention provides a layered oxide cathode material coated with MOF, its preparation method and a sodium-ion battery. To make the purpose, technical solution and effects of the present invention clearer and more definite, the present invention is further described in detail below. 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.

[0034] In practical applications, there are still some problems with the layered oxide cathode material. For example, during the high-voltage charge-discharge cycle process, phase transformation, gas generation, volume expansion, material peeling and other phenomena are likely to occur, thus affecting the stability and cycling performance of the battery. To address this problem, coating is considered a simple and effective method. The role of the coating is mainly to act as a protective layer to separate the electrolyte and the active material, reducing the occurrence of side reactions, which includes reducing the precipitation of oxygen atoms and reducing the rate of fragmentation and pulverization of the cathode material, thereby enhancing its electrochemical stability. In addition, by selecting an appropriate coating material, the transport efficiency of sodium ions, electronic conductivity and thermal stability can be significantly improved, thereby improving the rate performance and cycling stability of the battery.

[0035] Metal-organic framework (MOF) materials have characteristics such as porous structure, high specific surface area and adjustable chemical composition, making them have broad application prospects in the field of sodium-ion batteries. The large pore size, high specific surface area and stable structure of MOF materials, as a coating layer covering the surface of the layered oxide, can provide a diffusion channel for the transport of sodium ions and improve the migration rate of sodium ions; at the same time, as a coating layer material, MOF can adjust the oxygen defect concentration on the surface of the layered oxide cathode material, which is beneficial to improving the reversibility of oxygen anion redox, and thus improving the coulombic efficiency and cycling stability of the battery during charge and discharge under high-voltage conditions.

[0036] Based on this, an embodiment of the present invention provides a method for preparing a MOF-coated layered oxide cathode material, which includes the following steps:

[0037] (1) Ball-mill and mix a metal source and a sodium source, then calcine, and after cooling, obtain a layered oxide cathode material;

[0038] (2) Add an Mn salt or an Al salt and 2,5-dihydroxyterephthalic acid into a mixed solvent composed of dimethylformamide, ethanol, and deionized water, stir, then transfer to a reaction kettle for reaction, and purify the obtained suspension solution to obtain a MOF material;

[0039] (3) Mix the layered oxide cathode material obtained in step (1) and the MOF material obtained in step (2), and after heat treatment, obtain a MOF-coated layered oxide cathode material.

[0040] Compared with the prior art, the embodiment of the present invention has the following beneficial effects:

[0041] (1) MOF, as a coating layer material, has a large pore structure, provides a diffusion channel for the transport of sodium ions, and improves the migration rate of sodium ions.

[0042] (2) Mn-MOF or Al-MOF, as a coating layer material, can adjust the surface oxygen defect concentration of the layered oxide cathode material, which is beneficial to improving the reversibility of oxygen anion redox, and further improving the coulomb efficiency (manifested in excellent rate discharge performance) and cycle stability (manifested in high capacity retention rate) of the battery during charge and discharge under high voltage conditions.

[0043] (3) The preparation method of the embodiment of the present invention is simple in operation and novel in design, providing a new idea for the coating means.

[0044] In one embodiment, in step (1), the sodium source is sodium carbonate or sodium hydroxide; the metal source includes a TM source and manganese dioxide, and the TM source is at least one of hydroxides of Li, oxides of Mg, oxides of Al, oxides of K, oxides of Ca, oxides of Cu, oxides of Sn, oxides of Y, oxides of Nb, oxides of Ni, oxides of Fe, oxides of Zn, oxides of Ti, oxides of Co. As an example, the TM source can be magnesium oxide.

[0045] In one embodiment, in step (1), the ball milling speed is 200 - 600 r / min (such as 300 r / min, 500 r / min, etc.), and the ball milling time is 2 - 10 h (such as 5 h, 7 h, 9 h, etc.); the calcination temperature is 600 - 1000 °C (such as 700 °C, 800 °C, 900 °C, etc.), and the calcination time is 12 - 24 h (such as 15 h, 17 h, 18 h, 20 h, etc.).

[0046] In one embodiment, in step (1), the chemical formula of the layered oxide cathode material is Na x TM y Mn 1- y O2, where 0.5 ≤ x ≤ 1.1, 0 ≤ y ≤ 0.7, and TM is at least one of Li, Mg, Al, K, Ca, Cu, Sn, Y, Nb, Ni, Fe, Zn, Ti, Co. By way of example, the Na x TM y Mn 1-y O2 can be Na 0.8 Li 0.2 Mn 0.8 O2, Na 0.8 Mg 0.25 Mn 0.75 O2, etc., but not limited thereto.

[0047] Preferably, the Na x TM y Mn 1-y O2 is Na 0.8 Li 0.2 Mn 0.8 O2, Na 0.8 Mg 0.25 Mn 0.75 O2. The oxygen atoms of this type of material can participate in the redox reaction, that is, during the charge and discharge process, the oxygen atoms can change their oxidation state, thereby realizing the transfer of electrons and improving the capacity of the battery.

[0048] In one embodiment, step (2) specifically includes: adding a metal salt and 2,5-dihydroxyterephthalic acid to a mixed solvent composed of dimethylformamide, ethanol, and deionized water, stirring evenly, transferring to a reaction kettle for reaction, centrifuging the resulting suspension solution, washing with a solvent, and finally drying under vacuum to remove the solvent to obtain the MOF material.

[0049] In one embodiment, in step (2), the Mn salt can be manganese chloride tetrahydrate, etc., but not limited thereto.

[0050] In one embodiment, in step (2), the Al salt can be aluminum chloride hexahydrate, etc., but not limited thereto.

[0051] In one embodiment, in step (2), the volume ratio of dimethylformamide, ethanol and deionized water in the mixed solvent is 15 - 30:1:1.

[0052] In one embodiment, in step (2), the reaction temperature of the reaction kettle is 50 - 150 °C (such as 60 °C, 80 °C, 90 °C, 120 °C, etc.), and the reaction time is 5 - 20 h (such as 5 h, 7 h, 9 h, 12 h, 18 h, 20 h, etc.).

[0053] In one embodiment, in step (3), the mass ratio of the layered oxide cathode material to the MOF material is 1:0.005 - 0.1 (such as 1:0.005, 1:0.01, 1:0.05, 1:0.08, 1:0.09, etc.), the heat treatment temperature is 300 - 600 °C (such as 360 °C, 450 °C, 500 °C, 550 °C, etc.), and the heat treatment time is 3 - 6 h (such as 4 h, 5 h, 6 h, etc.).

[0054] The embodiment of the present invention provides a layered oxide cathode material coated with MOF, which is prepared by the method described in the embodiment of the present invention.

[0055] The embodiment of the present invention provides a sodium ion battery, including a positive electrode sheet, wherein the positive electrode sheet includes the layered oxide cathode material coated with MOF described in the embodiment of the present invention.

[0056] The present invention will be further described in detail below through several specific embodiments.

[0057] Example 1

[0058] A Na 0.8 Li 0.2 Mn 0.8 O2 layered oxide cathode material, and its preparation method includes the following steps:

[0059] (1) Synthesis of Na 0.8 Li 0.2 Mn 0.8 O2 layered oxide cathode material: Mix 0.4 mmol of sodium carbonate, 0.2 mmol of lithium hydroxide monohydrate, and 0.8 mmol of manganese dioxide evenly, ball mill for 5 h under the condition of 300 r / min, and dry the ball-milled sample in an oven at 60 °C for 12 h. Take the dried sample and sinter it at 700 °C for 15 h, and after cooling, obtain Na 0.8 Li 0.2 Mn 0.8 O2 layered oxide cathode material;

[0060] (2) Synthesis of Mn-MOF material: Add 34 mL of a mixed solvent of dimethylformamide / ethanol / deionized water into a 50 mL beaker, then add 16.5 mg of 2,5-dihydroxyterephthalic acid and 16.8 mg of manganese chloride tetrahydrate. Stir for 2 h under the condition of a stirring speed of 400 r / min. After complete dissolution, transfer it to a reaction kettle and react at 120 °C for 6 h. After cooling to room temperature, centrifuge the obtained suspension, wash it three times with N,N-dimethylformamide solution, and then dry it under vacuum at 200 °C for 5 h to remove the solvent. After cooling, the Mn-MOF material is obtained;

[0061] (3) Synthesis of Na 0.8 Li 0.2 Mn 0.8 O2 layered oxide cathode material coated with Mn-MOF: Mix the Na 0.8 Li 0.2 Mn 0.8 O2 obtained in step (1) and the Mn-MOF (2.0 wt%) obtained in step (2) evenly on a mortar, and then perform heat treatment at 300 °C for 5 h. After cooling, the Na 0.8 Li 0.2 Mn 0.8 O2 layered oxide cathode material coated with Mn-MOF is obtained.

[0062] Figure 1 The XRD pattern of the Na 0.8 Li 0.2 Mn 0.8 O2 layered oxide cathode material coated with Mn-MOF prepared in this example.

[0063] Example 2

[0064] A Na 0.8 Mg 0.25 Mn 0.75 O2 layered oxide cathode material coated with Mn-MOF, and its preparation method includes the following steps:

[0065] (1) Synthesis of Na 0.8 Mg 0.25 Mn 0.75 O2 layered oxide cathode material: Mix 0.4 mmol of sodium carbonate, 0.25 mmol of magnesium oxide, and 0.75 mmol of manganese dioxide evenly, ball mill for 5 h under the condition of 300 r / min, and dry the ball-milled sample in an oven at 60 °C for 12 h. Take the dried sample and sinter it at 800 °C for 12 h. After cooling, the Na 0.8 Mg 0.25 Mn 0.75 O2 layered oxide cathode material is obtained;

[0066] (2) Synthesis of Mn-MOF material: Add 34 mL of a mixed solvent of dimethylformamide / ethanol / deionized water into a 50 mL beaker, then add 16.5 mg of 2,5-dihydroxyterephthalic acid and 16.8 mg of manganese chloride tetrahydrate. Stir for 2 h under the condition of a stirring speed of 400 r / min. After complete dissolution, transfer it to a reaction kettle and react at 120 °C for 6 h. After cooling to room temperature, centrifuge the obtained suspension solution, wash it three times with N,N-dimethylformamide solution, and then dry it under vacuum at 200 °C for 5 h to remove the solvent. After cooling, the Mn-MOF material is obtained;

[0067] (3) Na 0.8 Mg 0.25 Mn 0.75 Synthesis of Mn-MOF-coated Na 0.8 Mg 0.25 Mn 0.75 O2 layered oxide cathode material: Mix the Na 0.8 Mg 0.25 Mn 0.75 O2 obtained in step (1) and the Mn-MOF (2.0 wt%) obtained in step (2) evenly on a mortar, and then perform heat treatment at 300 °C for 5 h. After cooling, the Mn-MOF-coated Na

[0068] Figure 2 XRD pattern of the Mn-MOF-coated Na 0.8 Mg 0.25 Mn 0.75 O2 layered oxide cathode material prepared in this example.

[0069] Example 3

[0070] An Al-MOF-coated Na 0.8 Li 0.2 Mn 0.8 O2 layered oxide cathode material, and its preparation method includes the following steps:

[0071] (1) Synthesis of Na 0.8 Li 0.2 Mn 0.8 O2 layered oxide cathode material: Mix 0.4 mmol of sodium carbonate, 0.2 mmol of lithium hydroxide monohydrate, and 0.8 mmol of manganese dioxide evenly, ball mill for 5 h under the condition of 300 r / min, and dry the ball-milled sample in an oven at 60 °C for 12 h. Take the dried sample and sinter it at 700 °C for 15 h. After cooling, the Na 0.8 Li 0.2 Mn 0.8 O2 layered oxide cathode material is obtained;

[0072] (2) Synthesis of Al-MOF material: Add 34 mL of a mixed solvent of dimethylformamide / ethanol / deionized water into a 50 mL beaker, then add 12 mg of 2,5-dihydroxyterephthalic acid and 15.7 mg of aluminum chloride hexahydrate, stir for 2 h under the condition of a stirring speed of 400 r / min, transfer to a reaction kettle after complete dissolution, react at 150 °C for 10 h, after cooling to room temperature, centrifuge the obtained suspension, wash three times with N,N-dimethylformamide solution, and then dry in vacuum at 200 °C for 5 h to remove the solvent. After cooling, the Al-MOF material is obtained;

[0073] (3) Na 0.8 Li 0.2 Mn 0.8 Synthesis of the layered oxide cathode material of LiMn₂O₄ coated with Al-MOF: Mix the Na 0.8 Li 0.2 Mn 0.8 O₂ obtained in step (1) and the Al-MOF (1.0 wt%) obtained in step (2) evenly on a mortar, and then perform heat treatment at 400 °C for 5 h. After cooling, the layered oxide cathode material of Na 0.8 Li 0.2 Mn 0.8 O₂ coated with Al-MOF is obtained.

[0074] Figure 3 SEM image of the layered oxide cathode material of Na 0.8 Li 0.2 Mn 0.8 O₂ coated with Al-MOF prepared in this example.

[0075] Example 4

[0076] A layered oxide cathode material of Na 0.8 Mg 0.25 Mn 0.75 O₂ coated with Al-MOF, and its preparation method includes the following steps:

[0077] (1) Synthesis of the layered oxide cathode material of Na 0.8 Mg 0.25 Mn 0.75 O₂: Mix 0.4 mmol of sodium carbonate, 0.25 mmol of magnesium oxide, and 0.75 mmol of manganese dioxide evenly, ball mill for 5 h under the condition of 300 r / min, and dry the ball-milled sample in an oven at 60 °C for 12 h. Take the dried sample and sinter at 800 °C for 12 h. After cooling, Na 0.8 Mg 0.25 Mn 0.75O2 layered oxide cathode material;

[0078] (2) Synthesis of Al-MOF material: Add 34 mL of a mixed solvent of dimethylformamide / ethanol / deionized water into a 50 mL beaker, then add 12 mg of 2,5-dihydroxyterephthalic acid and 15.7 mg of aluminum chloride hexahydrate, stir for 2 h under the condition of a stirring speed of 400 r / min, transfer to a reaction kettle after complete dissolution, react at 150 °C for 10 h, after cooling to room temperature, centrifuge the obtained suspension, wash three times with N,N-dimethylformamide solution, and then dry in vacuum at 200 °C for 5 h to remove the solvent. After cooling, obtain the Al-MOF material;

[0079] (3) Al-MOF-coated Na 0.8 Mg 0.25 Mn 0.75 Synthesis of O2 layered oxide cathode material: Mix the Na 0.8 Mg 0.25 Mn 0.75 O2 obtained in step (1) and the Al-MOF (1.0 wt%) obtained in step (2) evenly on a mortar, then perform heat treatment at 400 °C for 5 h. After cooling, obtain the Al-MOF-coated Na 0.8 Mg 0.25 Mn 0.75 O2 layered oxide cathode material.

[0080] Figure 4 SEM image of the Al-MOF-coated Na 0.8 Mg 0.25 Mn 0.75 O2 layered oxide cathode material prepared in this example.

[0081] Example 5

[0082] A Mn-MOF-coated Na 0.8 Li 0.2 Mn 0.8 O2 layered oxide cathode material, and its preparation method includes the following steps:

[0083] (1) Synthesis of Na 0.8 Li 0.2 Mn 0.8 O2 layered oxide cathode material: Mix 0.42 mmol of sodium carbonate, 0.21 mmol of lithium hydroxide monohydrate, and 0.8 mmol of manganese dioxide evenly, ball mill for 5 h under the condition of 300 r / min, and dry the ball-milled sample in an oven at 60 °C for 12 h. Take the dried sample and sinter at 800 °C for 15 h. After cooling, obtain Na 0.8 Li 0.2 Mn0.8 O2 layered oxide cathode material;

[0084] (2) Synthesis of Mn-MOF material: Add 34 mL of a mixed solvent of dimethylformamide / ethanol / deionized water into a 50 mL beaker, then add 16.5 mg of 2,5-dihydroxyterephthalic acid and 16.8 mg of manganese chloride tetrahydrate, stir for 2 h under the condition of a stirring speed of 400 r / min, transfer to a reaction kettle after complete dissolution, react at 120 °C for 6 h, after cooling to room temperature, centrifuge the obtained suspension solution, wash three times with N,N-dimethylformamide solution, and then dry in vacuum at 200 °C for 5 h to remove the solvent. After cooling, obtain the Mn-MOF material;

[0085] (3) Mn-MOF-coated Na 0.8 Li 0.2 Mn 0.8 Synthesis of O2 layered oxide cathode material: Mix the Na 0.8 Li 0.2 Mn 0.8 O2 obtained in step (1) and the Mn-MOF (1.0 wt%) obtained in step (2) evenly on a mortar, and then perform heat treatment at 300 °C for 5 h. After cooling, obtain the Mn-MOF-coated Na 0.8 Li 0.2 Mn 0.8 O2 layered oxide cathode material.

[0086] Example 6

[0087] A Mn-MOF-coated Na 0.8 Mg 0.25 Mn 0.75 O2 layered oxide cathode material, and its preparation method includes the following steps:

[0088] (1) Synthesis of Na 0.8 Mg 0.25 Mn 0.75 O2 layered oxide cathode material: Mix 0.42 mmol of sodium carbonate, 0.25 mmol of magnesium oxide, and 0.75 mmol of manganese dioxide evenly, ball mill for 5 h under the condition of 300 r / min, dry the ball milled sample in an oven at 60 °C for 12 h. Take the dried sample and sinter at 900 °C for 15 h. After cooling, obtain Na 0.8 Mg 0.25 Mn 0.75 O2 layered oxide cathode material;

[0089] (2) Synthesis of Mn-MOF material: Add 34 mL of a mixed solvent of dimethylformamide / ethanol / deionized water into a 50 mL beaker, then add 16.5 mg of 2,5-dihydroxyterephthalic acid and 16.8 mg of manganese chloride tetrahydrate. Stir for 2 h at a stirring speed of 400 r / min. After complete dissolution, transfer the solution to a reaction kettle and react at 120 °C for 6 h. After cooling to room temperature, centrifuge the obtained suspension, wash it three times with N,N-dimethylformamide solution, and then dry it in vacuum at 200 °C for 5 h to remove the solvent. After cooling, the Mn-MOF material is obtained;

[0090] (3) Synthesis of Na 0.8 Mg 0.25 Mn 0.75 O2 layered oxide cathode material coated with Mn-MOF: Mix the Na 0.8 Mg 0.25 Mn 0.75 O2 obtained in step (1) and the Mn-MOF (1.0 wt%) obtained in step (2) uniformly on a mortar, and then perform heat treatment at 300 °C for 5 h. After cooling, the Na 0.8 Mg 0.25 Mn 0.75 O2 layered oxide cathode material coated with Mn-MOF is obtained.

[0091] Application Example 1

[0092] A sodium-ion battery, the preparation method of which includes the following steps:

[0093] (1) Use the Na 0.8 Li 0.2 Mn 0.8 O2 coated with Mn-MOF obtained in Example 1 as the positive electrode active material, mix it with conductive carbon black and polyvinylidene fluoride (PVdF) binder in a mass ratio of 8:1:1, dissolve it in N-methylpyrrolidone (NMP) solvent to make a positive electrode slurry, and coat it on aluminum foil, dry and cut to obtain a positive electrode sheet;

[0094] (2) Assemble the positive electrode sheet obtained in step (1) with sodium metal and a glass fiber separator to form a sodium-ion battery. The electrolyte of this sodium-ion battery is an electrolyte formed by dissolving 1 M NaClO4 in PC (propylene carbonate). After assembly, let it stand for 12 h, and then perform electrochemical performance testing on it.

[0095] Specifically, the test method is: Perform a diffusion rate test of Na -1 at the positive electrode at a current density of 10 mAg + within a voltage range of 1.5 - 4.5 V.

[0096] At the same time, its cycling performance was tested.

[0097] Specifically, the test method was as follows: charging was carried out at a current density of 10 mA g -1 within the voltage range of 1.5 - 4.5 V, and discharging was carried out at a current density of 10 mA g -1 in sequence for 50 cycles to test the cycling performance.

[0098] At the same time, its rate performance was tested.

[0099] Specifically, the test method was as follows: charging was carried out at a current density of 10 mA g -1 within the voltage range of 1.5 - 4.5 V, and discharging was carried out at current densities of 10, 20, 50, 100, 500, and 10 mA g -1 in sequence for 5 cycles to test the rate performance.

[0100] Application Example 2

[0101] A sodium-ion battery, the preparation method of which includes the following steps:

[0102] (1) Using the Al-MOF-coated Na 0.8 Mg 0.25 Mn 0.75 O2 obtained in Example 4 as the positive electrode active material, mixing it with conductive carbon black and polyvinylidene fluoride (PVdF) binder in a mass ratio of 8:1:1, dissolving the mixture in N-methylpyrrolidone (NMP) solvent to make a positive electrode slurry, and coating it on aluminum foil, followed by drying and cutting to obtain a positive electrode sheet;

[0103] (2) Assembling the positive electrode sheet obtained in step (1) with sodium metal and a glass fiber separator to form a sodium-ion battery. The electrolyte of this sodium-ion battery is an electrolyte formed by dissolving 1 M NaClO4 in PC (propylene carbonate). After assembly, it was left standing for 12 h, and then its electrochemical performance was tested.

[0104] Specifically, the test method was as follows: cyclic voltammetry (CV) test was carried out at a scanning rate of 0.2 mV s -1 within the voltage range of 1.5 - 4.5 V.

[0105] At the same time, its cycling performance was tested.

[0106] Specifically, the test method was as follows: charging was carried out at a current density of 10 mA g -1 within the voltage range of 1.5 - 4.5 V, and discharging was carried out at a current density of 10 mA g -1 in sequence for 50 cycles to test the cycling performance.

[0107] At the same time, its rate performance was tested.

[0108] Specifically, the testing method is as follows: at a current density of 10 mA g -1 , charge within the voltage range of 1.5 - 4.5 V, and then discharge at current densities of 10, 20, 50, 100, 500, and 10 mA g -1 for 5 cycles in sequence to conduct the rate performance test.

[0109] Comparative Example 1

[0110] A sodium-ion battery, and its preparation method includes the following steps:

[0111] (1) Use the layered oxide Na 0.8 Li 0.2 Mn 0.8 O2 obtained in step (1) of Example 1 as the positive electrode active material. Mix it with conductive carbon black and polyvinylidene fluoride (PVdF) binder in a mass ratio of 8:1:1, then dissolve the mixture in N-methylpyrrolidone (NMP) solvent to make a positive electrode slurry, and coat it on aluminum foil, followed by drying and cutting to obtain the positive electrode sheet;

[0112] (2) Assemble the positive electrode sheet obtained in step (1) with sodium metal and a glass fiber separator to form a sodium-ion battery. The electrolyte of this sodium-ion battery is an electrolyte formed by dissolving 1 M NaClO4 in PC (propylene carbonate). After assembly, let it stand for 12 h, and then conduct electrochemical performance tests on it.

[0113] Specifically, the testing method is as follows: at a current density of 10 mA g -1 , conduct the Na + diffusion rate test at the positive electrode within the voltage range of 1.5 - 4.5 V.

[0114] At the same time, conduct a cycle performance test on it.

[0115] Specifically, the testing method is as follows: at a current density of 10 mA g -1 , charge within the voltage range of 1.5 - 4.5 V, and then discharge at a current density of 10 mA g -1 for 50 cycles in sequence to conduct the cycle performance test.

[0116] At the same time, conduct a rate performance test on it.

[0117] Specifically, the testing method is as follows: at a current density of 10 mA g -1 , charge within the voltage range of 1.5 - 4.5 V, and then discharge at current densities of 10, 20, 50, 100, 500, and 10 mA g -1 for 5 cycles in sequence to conduct the rate performance test.

[0118] Figure 5For the GITT curves and corresponding Na diffusion coefficients of the sodium-ion batteries in Application Example 1 and Comparative Example 1, it can be seen from + that the average diffusion rate of Na in the positive electrode of Application Example 1 is 9.18×10 Figure 5 , while that of Comparative Example 1 is 2.96×10 + , indicating that Application Example 1 has better kinetic performance. -11 For the cycling performance curves of the sodium-ion batteries in Application Example 1 and Comparative Example 1, it can be seen from + that under the conditions of a voltage range of 1.5 - 4.5V, a charging current density of 10 mA g -11 (0.1C), and a discharging current density of 10 mA g(0.1C), after 50 cycles, the battery capacity retention rate of Application Example 1 is still as high as 67.94%, while that of Comparative Example 1 is only 33.3%. At the same time, it can be seen that the average Coulombic efficiency of Application Example 1 is higher than that of Comparative Example 1.

[0119] Figure 6 Figure 6 -1 (0.1C), and a discharging current density of 10 mA g -1 (0.1C), after 50 cycles, the battery capacity retention rate of Application Example 1 is still as high as 67.94%, while that of Comparative Example 1 is only 33.3%. At the same time, it can be seen that the average Coulombic efficiency of Application Example 1 is higher than that of Comparative Example 1.

[0120] From the rate performance Figure 7 it can be known that the obtained Na 0.8 Li 0.2 Mn 0.8 O2 positive electrode material in Application Example 1 exhibits more excellent rate discharge performance than that in Comparative Example 1.

[0121] Comparative Example 2

[0122] A sodium-ion battery, the preparation method of which includes the following steps:

[0123] (1) Using the layered oxide Na 0.8 Mg 0.25 Mn 0.75 O2 obtained in step (1) of Example 2 as the positive electrode active material, mixing it with conductive carbon black and polyvinylidene fluoride (PVdF) binder in a mass ratio of 8:1:1, dissolving the mixture in N-methylpyrrolidone (NMP) solvent to make a positive electrode slurry, and coating it on an aluminum foil, followed by drying and cutting to obtain a positive electrode sheet;

[0124] (2) Assembling the positive electrode sheet obtained in step (1) with sodium metal and a glass fiber separator to form a sodium-ion battery. The electrolyte of this sodium-ion battery is an electrolyte formed by dissolving 1M NaClO4 in PC (propylene carbonate). After assembly, it is left standing for 12h, and then its electrochemical performance is tested.

[0125] Specifically, the test method is: at 0.2 mV s-1 The scanning rate was tested by cyclic voltammetry (CV) within the voltage range of 1.5 - 4.5 V.

[0126] Meanwhile, its cycling performance was tested.

[0127] Specifically, the test method was as follows: charging was carried out at a current density of 10 mA g -1 within the voltage range of 1.5 - 4.5 V, and discharging was carried out at a current density of 10 mA g -1 in sequence for 50 cycles to test the cycling performance.

[0128] Meanwhile, its rate performance was tested.

[0129] Specifically, the test method was as follows: charging was carried out at a current density of 10 mA g -1 within the voltage range of 1.5 - 4.5 V, and discharging was carried out at current densities of 10, 20, 50, 100, 500, and 10 mA g -1 in sequence for 5 cycles to test the rate performance.

[0130] Figure 8 Fig. is the CV curve of the sodium-ion batteries of Application Example 2 and Comparative Example 2. It can be seen from Figure 8 that the CV curves of the first 5 cycles of Application Example 2 have better coincidence than those of Comparative Example 2, with better reversibility, and Application Example 2 has better cycling stability.

[0131] Figure 9 Fig. is the cycling performance curve of the sodium-ion batteries of Application Example 2 and Comparative Example 2. It can be seen from Figure 9 that within the voltage range of 1.5 - 4.5 V, with a charging current density of 10 mA g -1 (0.1 C) and a discharging current density of 10 mA g -1 (0.1 C), after 50 cycles, the battery capacity retention rate of Application Example 2 is as high as 79.35%, while that of Comparative Example 2 is 66.39%. Meanwhile, it can be seen that the average Coulombic efficiency of Application Example 2 is higher than that of Comparative Example 2.

[0132] From the rate performance Figure 10 it can be known that the obtained Na 0.8 Mg 0.25 Mn 0.75 O2 cathode material of Application Example 2 with Al-MOF coating exhibits more excellent rate discharge performance than that of Comparative Example 2.

[0133] In summary, the present invention provides a layered oxide cathode material coated with MOF, a preparation method thereof, and a sodium ion battery. The MOF of the present invention has a large pore size structure as a coating material, providing a diffusion channel for the transport of sodium ions and enhancing the migration rate of sodium ions. As a coating material, MOF can adjust the surface oxygen defect concentration of the layered oxide cathode material, which is beneficial to improving the reversibility of oxygen anion redox, and further improving the coulomb efficiency and cycle stability of the battery during charge and discharge under high voltage conditions. The operation of the present invention is simple and the design is novel, providing a new idea for the coating method.

[0134] It should be understood that the application of the present invention is not limited to the above examples. For those of ordinary skill in the art, improvements or transformations can be made according to the above description, and all such improvements and transformations should fall within the protection scope of the appended claims of the present invention.

Claims

1. A preparation method of a MOF-coated layered oxide cathode material, characterized in that, It includes the following steps: (1) Ball-mill and mix a metal source and a sodium source, then calcine. After cooling, a layered oxide cathode material is obtained; (2) Add an Mn salt or an Al salt and 2,5-dihydroxyterephthalic acid into a mixed solvent composed of dimethylformamide, ethanol and deionized water, stir, then transfer to a reaction kettle for reaction. Purify the obtained suspension solution after the reaction to obtain a MOF material; (3) Mix the layered oxide cathode material obtained in step (1) and the MOF material obtained in step (2), and after heat treatment, a MOF-coated layered oxide cathode material is obtained.

2. The preparation method according to claim 1, wherein In step (1), the sodium source is sodium carbonate or sodium hydroxide; the metal source includes a TM source and manganese dioxide, and the TM source is at least one of hydroxides of Li, oxides of Mg, oxides of Al, oxides of K, oxides of Ca, oxides of Cu, oxides of Sn, oxides of Y, oxides of Nb, oxides of Ni, oxides of Fe, oxides of Zn, oxides of Ti, oxides of Co.

3. The preparation method according to claim 1, characterized in that, In step (1), the ball-milling speed is 200 - 600 r / min, and the ball-milling time is 2 - 10 h; the calcination temperature is 600 - 1000 °C, and the calcination time is 12 - 24 h.

4. The preparation method according to claim 1, characterized in that, In step (1), the chemical formula of the layered oxide cathode material is Na x TM y Mn 1-y O2, where 0.5 ≤ x ≤ 1.1, 0 ≤ y ≤ 0.7, and TM is at least one of Li, Mg, Al, K, Ca, Cu, Sn, Y, Nb, Ni, Fe, Zn, Ti, and Co.

5. The preparation method according to claim 1, characterized in that, In step (2), the Mn salt is manganese chloride tetrahydrate, and the Al salt is aluminum chloride hexahydrate.

6. The preparation method according to claim 1, wherein In step (2), the volume ratio of dimethylformamide, ethanol and deionized water in the mixed solvent is 15 - 30:1:

1.

7. The preparation method according to claim 1, wherein In step (2), the reaction temperature of the reaction kettle is 50 - 150 °C, and the reaction time is 5 - 20 h.

8. The preparation method according to claim 1, wherein In step (3), the mass ratio of the layered oxide cathode material to the MOF material is 1:0.005 - 0.1, the heat treatment temperature is 300 - 600 °C, and the heat treatment time is 3 - 6 h.

9. A MOF-coated layered oxide cathode material, characterized in that, Prepared by the method according to any one of claims 18.

10. A sodium-ion battery, comprising a positive electrode sheet, characterized in that, The positive electrode sheet includes the MOF-coated layered oxide cathode material according to claim 9.

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