Preparation method of coated and modified NaNi0. 5Mn0. 5O2 positive electrode material and material thereof

Abstract

The invention relates to the field of electrochemical materials, in particular to a preparation method of a coated and modified NaNi0. 5Mn0. 5O2 positive electrode material, which comprises the following steps: adding DMF (Dimethyl Formamide) into PTA (Pure Terephthalic Acid) in proportion by a solvothermal method to obtain a first mixed solution, then adding the DMF into Ni (NO) 3.6 H2O in proportion to prepare a second mixed solution, mixing and heating to obtain a precursor Ni-MOFs solution; the cooled precursor Ni-MOFs solution is centrifuged and then dried, and a precursor Ni-MOFs is obtained; the preparation method comprises the following steps: weighing Na2CO3, NiO and MnO2 reagents in proportion, mixing, fully grinding, heating to 500 DEG C for 12 hours, heating to 900 DEG C for 12 hours, and obtaining O3 type NaNi0. 5Mn0. 5O2; oxalic acid and the prepared O3 type NaNi0. 5Mn0. 5O2 are mixed to obtain a third mixed solution, then a precursor Ni-MOFs is added into the third mixed solution, and NaNi0. 5Mn0. 5O2 is obtained after drying and calcination. According to the invention, Ni-MOFs coated O3 type NaNi0. 5Mn0. 5O2 is taken as the sodium ion battery positive electrode material through a coprecipitation method, so that the sodium ion battery positive electrode material shows excellent cycle performance, and has relatively high stability in the aspect of capacity failure in a cycle.

Description

Technical Field

[0001] The present invention relates to the field of electrochemical materials, and particularly to a preparation method of a coated and modified NaNi 0.5 Mn 0.5 O2 cathode material and the material thereof. Background Art

[0002] With the rapid development of electronic products and low-power electric vehicles, higher requirements are put forward for energy storage materials in terms of energy efficiency, resource reserves, environmental friendliness, etc. Sodium-ion batteries (SIBs) have become a new energy material with broad prospects because of their low raw material cost and large reserves, and have more advantages compared with lithium-ion batteries. Currently, the most studied sodium-ion battery materials mainly focus on cathode materials, and layered transition metal oxides with high working voltage and electrochemical capacity have become a research hotspot. Among them, the O3-type layered oxide NaNi 0.5 Mn 0.5 O2 material is considered to have great development prospects because of its many advantages such as high capacity, high voltage, low cost, and simple synthesis route.

[0003] However, their actual application prospects are limited by several key disadvantages: the cycling performance of sodium-ion batteries is not ideal and the cycle life is short; the stability of sodium-ion batteries is insufficient. When the O3-type NaNi 0.5 Mn 0.5 O2 is exposed to air, active Na will escape from the lattice to the surface, accompanied by the formation of a Na-deficient phase and the oxidation of transition metal ions in the matrix.

[0004] Therefore, there is a need for a preparation method of a NaNi 0.5 Mn 0.5 O2 cathode material and the material thereof that can improve the cycle life and stability of sodium-ion batteries. Summary of the Invention

[0005] The main object of the present invention is to provide a preparation method of a coated and modified NaNi 0.5 Mn 0.5 O2 cathode material and the material thereof, aiming to solve the problem that the cycle life and stability of sodium-ion cathode materials in the prior art are difficult to meet commercial requirements.

[0006] To achieve the above object, the present invention proposes a preparation method of a coated and modified NaNi 0.5 Mn 0.5 O2 cathode material, and the method comprises the following steps: Prepare the precursor Ni-MOFs solution. By the solvothermal method, add DMF to PTA in proportion to obtain the first mixed solution, and then add DMF to Ni(NO)3·6H2O in proportion to prepare the second mixed solution. Mix the first mixed solution and the second mixed solution and heat to obtain the precursor Ni-MOFs solution; Prepare the precursor Ni-MOFs. Centrifuge the cooled precursor Ni-MOFs solution at 8500 rmp for 3 - 5 min, and wash it alternately with absolute ethanol and deionized water. After centrifuging 3 - 5 times, transfer it to a drying oven at 83 - 85 °C and dry for 5 - 7 h to obtain the precursor Ni-MOFs; Prepare O3-type NaNi 0.5 Mn 0.5 O2. Weigh Na2CO3, NiO, and MnO2 reagents in proportion. Mix the three reagents and transfer them to a ball mill for thorough grinding. Then transfer them to a tubular furnace and heat it at a heating rate of 5 °C / min to 500 °C and hold for 12 h. After holding for 12 h, continue to heat it to 900 °C at the same heating rate and hold for 12 h to obtain O3-type NaNi 0.5 Mn 0.5 O2; Prepare the coated and modified NaNi 0.5 Mn 0.5 O2. Mix oxalic acid and the prepared O3-type NaNi 0.5 Mn 0.5 O2 in deionized water by stirring to obtain the third mixed solution. Then add the precursor Ni-MOFs to the third mixed solution. Heat and evaporate the third mixed solution to obtain a paste material. Dry the paste material and calcine it for 24 h to obtain the coated and modified NaNi 0.5 Mn 0.5 O2.

[0007] Furthermore, the step of preparing the precursor Ni-MOFs solution, by the solvothermal method, adding DMF to PTA in proportion to obtain the first mixed solution, and then adding DMF to Ni(NO)3·6H2O in proportion to prepare the second mixed solution, mixing the first mixed solution and the second mixed solution and heating to obtain the precursor Ni-MOFs solution, further includes: Stir the first mixed solution and the second mixed solution for 5 min respectively to make the solutes in the first mixed solution and the second mixed solution dissolve fully; Mix the first mixed solution and the second mixed solution and continue to stir at 350 rmp for 30 min to obtain a turquoise transparent solution; Transfer the turquoise transparent solution to a reaction kettle and heat the reaction kettle to 120 °C and hold the reaction for 12 h; After the reaction, remove the reaction kettle and cool it naturally to room temperature to obtain the precursor Ni-MOFs solution.

[0008] Further, for the preparation of the coated and modified NaNi 0.5 Mn 0.5 O2, oxalic acid and the prepared O3-type NaNi 0.5 Mn 0.5 O2 are stirred and mixed in deionized water to obtain a third mixed solution, and then the precursor Ni-MOFs are added to the third mixed solution. After heating and evaporating the third mixed solution, a paste-like material is obtained. After drying the paste-like material, it is calcined for 24 h to obtain the coated and modified NaNi 0.5 Mn 0.5 O2. The steps include: For the preparation of the coated and modified NaNi 0.5 Mn 0.5 O2, oxalic acid and the prepared O3-type NaNi 0.5 Mn 0.5 O2 are stirred and mixed in deionized water to obtain a third mixed solution; Then, the precursor Ni-MOFs are added to the third mixed solution, and the third mixed solution incorporated with the precursor Ni-MOFs is transferred into an oil bath at 80 °C for stirring and evaporation to obtain a paste-like material; The paste-like material is placed in a vacuum oven and dried at 80 °C for 6 h to obtain a brown powder. Then, the brown powder is calcined in a tubular furnace at 900 °C for 24 h to obtain the coated and modified NaNi 0.5 Mn 0.5 O2.

[0009] Further, the mass ratio of oxalic acid to NaNi 0.5 Mn 0.5 O2 is 1.5:1.

[0010] The present invention also provides a coated and modified NaNi 0.5 Mn 0.5 O2 cathode material. The coated and modified NaNi0.5Mn0.5O2 cathode material is prepared by the preparation method of the coated and modified NaNi 0.5 Mn 0.5 O2 cathode material according to any one of the above technical solutions.

[0011] In the present invention, the O3-type NaNi 0.5 Mn 0.5 O2 sodium-ion battery cathode material coated with high-entropy layered oxide prepared by the co-precipitation method can improve the O3-type NaNi 0.5 Mn 0.5The rate performance and cycling performance of O2, avoiding the situation where active Na escapes from the lattice to the surface when O3-type NaNi 0.5 Mn 0.5 O2 is exposed to air, effectively improving the cycling life and stability of sodium-ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained according to the processes shown in these drawings.

[0013] Figure 1 Schematic flow chart of Example 1 in the preparation method of the coated and modified NaNi 0.5 Mn 0.5 O2 cathode material; Figure 2 Schematic flow chart of Example 1 in the preparation method of the coated and modified NaNi 0.5 Mn 0.5 XRD pattern of bare NaNi 0.5 Mn 0.5 O2; Figure 3 XRD patterns of the NaNi 0.5 Mn 0.5 coated by Example 1 and Comparative Example 1 in the preparation method of the coated and modified NaNi 0.5 Mn 0.5 O2 cathode material; Figure 4 First charge-discharge curves of Example 1 and Comparative Example 1 in the preparation method of the coated and modified NaNi 0.5 Mn 0.5 O2 cathode material; Figure 5 Cycling stability diagrams of Example 1 and Comparative Example in the preparation method of the coated and modified NaNi 0.5 Mn 0.5 O2 cathode material at 0.1C rate for 100 cycles; Figure 6 CV diagram of Comparative Example 1 in the preparation method of the coated and modified NaNi 0.5 Mn 0.5 O2 cathode material; Figure 7 Schematic flow chart of Example 1 in the preparation method of the coated and modified NaNi 0.5 Mn0.5 CV diagram of Example 1 in the preparation method of O2 cathode material. Detailed implementation manners

[0014] Next, in combination with the embodiments of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0015] It should be noted that all directional indications (such as up, down, left, right, front, back...) in the embodiments of the present invention are only used to explain the relative positional relationship and movement conditions between components in a specific posture. If the specific posture changes, the directional indication will also change accordingly.

[0016] In addition, the descriptions involving "first", "second", etc. in the present invention are only for descriptive purposes, and cannot be understood as indicating or implying their relative importance or implicitly indicating the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include at least one of such features. In addition, the technical solutions between various embodiments can be combined with each other, but it must be based on the ability of those of ordinary skill in the art to implement. When the combination of technical solutions results in contradictions or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0017] NaNi 0.5 Mn 0.5 The surface of the NaNi 0.5 Mn 0.5 O2 material is often coated and modified by a simple physical method. Through this method, the cycle performance and rate performance of sodium-ion batteries can be improved to a certain extent. However, not only the improvement degree is limited, but also the structure of the parent material NaNi

[0018] In the present invention, the NaNi 0.5 Mn 0.5 O2 material prepared by the co-precipitation method has better cycle performance and rate performance compared with the prior art, and as Figures 2 to 3 shown, the XRD results can show that the structure of the parent material will not be damaged. Through the technical solutions disclosed in the present invention, it can be seen that the NaNi 0.5 Mn 0.5Side effects between the O2 material and the electrolyte to enhance the stability of sodium-ion batteries. In addition, due to the excellent electrical conductivity and structural stability of the high-entropy oxide itself, the rate performance after coating the NaNi 0.5 Mn 0.5 O2 material is improved.

[0019] The coated and modified NaNi 0.5 Mn 0.5 O2 cathode material disclosed in the present invention, as Figure 1 shown, the specific steps are as follows: S10. Prepare the precursor Ni-MOFs solution. By the solvothermal method, add DMF to PTA in proportion to obtain the first mixed solution, and then add DMF to Ni(NO)3·6H2O in proportion to prepare the second mixed solution. Mix the first mixed solution and the second mixed solution and heat to obtain the precursor Ni-MOFs solution; S20. Prepare the precursor Ni-MOFs. Centrifuge the cooled precursor Ni-MOFs solution at 8500 rmp for 3 - 5 min, and wash it alternately with absolute ethanol and deionized water. After centrifuging 3 - 5 times, transfer it to a drying oven at 83 - 85 °C and dry for 5 - 7 h to obtain the precursor Ni-MOFs; S30. Prepare the O3-type NaNi 0.5 Mn 0.5 O2. Weigh Na2CO3, NiO, and MnO2 reagents in proportion. Mix the three reagents and transfer them to a ball mill for sufficient grinding, and then transfer them to a tubular furnace and heat at a heating rate of 5 °C / min to 500 °C for 12 h. After 12 h, continue to heat at the same heating rate to 900 °C and hold for 12 h to obtain the O3-type NaNi 0.5 Mn 0.5 O2; S40. Prepare the coated and modified NaNi 0.5 Mn 0.5 O2. Stir and mix oxalic acid and the prepared O3-type NaNi 0.5 Mn 0.5 O2 in deionized water to obtain the third mixed solution. Then add the precursor Ni-MOFs to the third mixed solution. Heat and evaporate the third mixed solution to obtain a paste material. Dry the paste material and calcine it for 24 h to obtain the coated and modified NaNi 0.5 Mn 0.5 O2.

[0020] Among them, the high-entropy oxide involved in the present invention is the abbreviation of Ni-MOFs material, where Ni-MOFs is a nickel metal-organic framework, which forms a crystal porous structure after the coordination of nickel ions and organic ligands. The PTA involved in the present invention is pure terephthalic acid, and the specific chemical formula is as follows:

[0021] The DMF involved in the present invention is N,N-dimethylformamide, and the specific chemical formula is as follows:

[0022] Among them, the present invention also discloses specific application examples 1-3 and comparative example 1. Examples 1-3 and comparative example 1 are NaNi 0.5 Mn 0.5 O2 cathode materials coated and modified with high-entropy oxides obtained by different preparation methods, and the specific preparation is as follows: Example 1

[0023] S1. Prepare the precursor Ni-MOFs solution. By the solvothermal method, add 15 ml of DMF to 0.4984 g of PTA, and then add 10 ml of DMF to 0.8724 g of Ni(NO)3·6H2O. Stir for 5 minutes respectively to make them fully dissolved, and prepare the first mixed solution and the second mixed solution. Mix the first mixed solution and the second mixed solution and heat to obtain the precursor Ni-MOFs solution; S2. Prepare the precursor Ni-MOFs. Centrifuge the cooled precursor Ni-MOFs solution at 8500 rmp for 3 minutes, and wash it alternately with anhydrous ethanol and deionized water. After centrifuging 5 times, transfer it to a drying oven at 83 °C for drying for 6 hours to obtain the precursor Ni-MOFs; S3. Prepare O3-type NaNi 0.5 Mn 0.5 O2. Weigh 3.387 g of Na2CO3, 2.24 g of NiO and 2.61 g of MnO2 reagents. Mix the three reagents and transfer them to a ball mill for sufficient grinding, and then transfer them to a tubular furnace and heat them at a heating rate of 5 °C / min to 500 °C for 12 hours. After 12 hours, continue to heat them to 900 °C at the same heating rate and keep it for 12 hours to obtain O3-type NaNi 0.5 Mn 0.5 O2; S4. Prepare the coated and modified NaNi 0.5 Mn 0.5 O2, calculate the required amount of oxalic acid (oxalic acid: O3-type NaNi 0.5 Mn 0.5O2=1.5:1), and oxalic acid and the prepared O3-type NaNi 0.5 Mn 0.5 O2 is stirred and mixed in deionized water to obtain a third mixed solution, and then 10% by weight of Ni-MOFs, a precursor of high entropy layered oxide, is added to the third mixed solution under stirring, and the third mixed solution is stirred and evaporated in an oil bath at 80° C. to become a paste; S5. The paste material was placed in a vacuum oven and dried at 80°C for 6 h to obtain a brown powder. The brown powder was then placed in a tube furnace and heated at a heating rate of 5°C / min. After the temperature was raised to 900°C, it was calcined for 24 h to obtain the coated modified NaNi 0.5 Mn 0.5 O2, denoted as CP-10. Example 2

[0024] S1. Preparing a precursor Ni-MOFs solution, by a solvothermal method, adding 12 ml of DMF to 0.6281 g of PTA, and then adding 10 ml of DMF to 1.047 g of Ni(NO)3·6H2O, stirring for 5 min to fully dissolve them, respectively, to prepare a first mixed solution and a second mixed solution, mixing the first mixed solution with the second mixed solution and heating to obtain a precursor Ni-MOFs solution; S2. Preparing precursor Ni-MOFs, centrifuging the cooled precursor Ni-MOFs solution at 6500 rpm for 5 min, washing with anhydrous ethanol and deionized water alternately, centrifuging for 3 times, and then transferring to a drying oven at 84° C. for drying for 5 h to obtain precursor Ni-MOFs; S3. Preparation of O3-type NaNi 0.5 Mn 0.5 O2, weigh 4.064g Na2CO3, 2.69g NiO and 3.13g MnO2 reagents, mix the three reagents and move them into a ball mill for thorough grinding, then move them into a tube furnace and heat them to 500℃ at a heating rate of 5℃ / min for 12h, then continue to heat them to 900℃ at the same heating rate for 12h to obtain O3 type NaNi 0.5 Mn 0.5 O2; S4. Preparation of coated modified NaNi 0.5 Mn 0.5 O2, calculate the demand for oxalic acid (oxalic acid: O3 type NaNi 0.5 Mn 0.5 O2=2:1), and oxalic acid and the prepared O3-type NaNi 0.5 Mn 0.5O2 is stirred and mixed in deionized water to obtain a third mixed solution, and then Ni-MOFs, a precursor of a high entropy layered oxide, is added to the third mixed solution in a mass ratio of 12% under stirring, and the third mixed solution is stirred and evaporated in an oil bath at 80° C. to become a paste; S5. The paste material was placed in a vacuum oven and dried at 80°C for 6 h to obtain a brown powder. The brown powder was then placed in a tube furnace and heated at a heating rate of 5°C / min. After the temperature was raised to 900°C, it was calcined for 24 h to obtain the coated modified NaNi 0.5 Mn 0.5 O2, denoted as CP-20. Example 3

[0025] S1. Preparing a precursor Ni-MOFs solution, by a solvothermal method, adding 15 ml of DMF to 0.752 g of PTA, and then adding 10 ml of DMF to 1.22 g of Ni(NO)3·6H2O, stirring for 5 min to fully dissolve them, respectively, to prepare a first mixed solution and a second mixed solution, mixing the first mixed solution and the second mixed solution and heating them to obtain a precursor Ni-MOFs solution; S2. Preparing precursor Ni-MOFs, centrifuging the cooled precursor Ni-MOFs solution at 8500 rpm for 5 min, washing it alternately with anhydrous ethanol and deionized water, centrifuging it 4 times, and then transferring it into a drying oven at 84°C for drying for 5 h to obtain precursor Ni-MOFs; S3. Preparation of O3-type NaNi 0.5 Mn 0.5 O2, weigh 5.081g Na2CO3, 3.16g NiO and 3.92g MnO2 reagents, mix the three reagents and move them into a ball mill for thorough grinding, then move them into a tube furnace and heat them to 500℃ at a heating rate of 5℃ / min for 12h, then continue to heat them to 900℃ at the same heating rate for 12h to obtain O3 type NaNi 0.5 Mn 0.5 O2; S4. Preparation of coated modified NaNi 0.5 Mn 0.5 O2, calculate the demand for oxalic acid (oxalic acid: O3 type NaNi 0.5 Mn 0.5 O2=1.2:1), and oxalic acid and the prepared O3-type NaNi 0.5 Mn 0.5 O2 is stirred and mixed in deionized water to obtain a third mixed solution, and then 10% by weight of Ni-MOFs, a precursor of high entropy layered oxide, is added to the third mixed solution under stirring, and the third mixed solution is stirred and evaporated in an oil bath at 80° C. to become a paste; S5. Place the paste material in a vacuum oven and dry it at 80 °C for 6 h to obtain a brown powder. Then, place the brown powder in a tube furnace and heat it at a heating rate of 5 °C / min. After heating to 900 °C, calcine it for 24 h to obtain the coated and modified NaNi 0.5 Mn 0.5 O2, denoted as CP-30.

[0026] Comparative Example 1: S1. Prepare the precursor Ni-MOFs solution. By the solvothermal method, add DMF proportionally to PTA to obtain the first mixed solution, and then add DMF proportionally to Ni(NO)3·6H2O to prepare the second mixed solution. Mix the first mixed solution and the second mixed solution and heat to obtain the precursor Ni-MOFs solution S2. Prepare the precursor Ni-MOFs. Centrifuge the cooled precursor Ni-MOFs solution at 8500 rmp for 3 - 5 min, and wash it alternately with absolute ethanol and deionized water. After centrifuging 3 - 5 times, transfer it to a drying oven at 83 - 85 °C and dry it for 5 - 7 h to obtain the precursor Ni-MOFs; S3. Prepare O3-type NaNi 0.5 Mn 0.5 O2. Weigh Na2CO3, NiO, and MnO2 reagents proportionally. Mix the three reagents and transfer them to a ball mill for sufficient grinding. Then, transfer them to a tube furnace and heat at a heating rate of 5 °C / min to 500 °C for 12 h. After 12 h, continue to heat at the same heating rate to 900 °C and keep it for 12 h to obtain O3-type NaNi 0.5 Mn 0.5 O2; S4. Place the prepared bare NaNi 0.5 Mn 0.5 O2 powder and Ni-MOFs high-entropy oxide nanoparticles in a polypropylene bottle with an appropriate amount of zirconia balls, and mix them using a ball mill; S5. Heat in a tube furnace at a heating rate of 5 °C / min to 900 °C and calcine for 24 h. After the calcination, let the sample cool naturally to room temperature in the furnace. Place the cooled product in a glove box under an argon atmosphere for storage; Among them, the molar ratio of the Ni-MOFs high-entropy oxide coating material to the parent NaNi 0.5 Mn 0.5 O2 is 1:10, denoted as BM-10.

[0027] It can be understood that from Examples 1 - 3 and Comparative Example 1, it can be seen that there are significant differences between the present invention and the prior art in the wrapping method of high-entropy oxides. The present invention has better electrical properties than the prior art.

[0028] Specifically, as Figures 2 to 3 shown, Figure 2 is the XRD pattern of the unmodified NaNi 0.5 Mn 0.5 O2 material, Figure 3 taking Comparative Example 1 (BM-10 shown in the figure) and Example 1 (CP-10 shown in the figure) disclosed in the present invention as references, which can show that the XRD diffraction peaks of the modified NaNi 0.5 Mn 0.5 O2 material can completely correspond to those of the unmodified NaNi 0.5 Mn 0.5 O2 material. At the same time, the lattice spacing obtained by high-resolution TEM further proves that the coating of high-entropy oxide does not affect the crystal structure of the material. Specifically, the method disclosed in Comparative Example 1 is the physical ball milling method.

[0029] To illustrate the performance differences of different coating methods on sodium-ion cathode materials, electrochemical tests were carried out on Example 1 and Comparative Example 1 using coin cells. The specific steps of the electrochemical tests are as follows: Step S100: Cut the battery separator into the original piece corresponding to the coin cell, and place it in a vacuum drying oven for drying for 24 h. The drying pressure is -0.1 MPa, and the temperature is 50-60 °C. After drying, place it in a glove box for standby; Step S200: Wash the shell of the coin cell with anhydrous ethanol, place it in a vacuum drying oven to evacuate, and then dry it with a blast drying oven. After that, place the shell in a glove box for standby; Step S300: Prepare a solution with a mass percentage concentration of 7.5% using PVDF as the solute and NMP as the solvent as the binder, and then prepare the electrolyte and negative electrode sheet of the coin cell and place them in a glove box for standby; Step S400: Under the condition that the H2O concentration in the glove box is lower than 10 ppm, place the foamed nickel, positive electrode sheet, separator, and negative electrode sheet in the battery shell in sequence. After compaction, seal it with a sealer and let it stand for 14-16 h after sealing; Step S500: Discharge the assembled battery at a constant current to 5 mV, let it stand for 10 min, then discharge it at a constant current to 5 mV, and then discharge it at a constant current to 2.0 V. The current is 0.6 mA (under the condition of 0.1C), and record the discharge capacity and charge capacity during this process; Step S600: Calculate the mass of the active material on the electrode sheet, and then calculate the charge-discharge specific capacity. The unit of the charge-discharge specific capacity is mAh / g. The first charge-discharge efficiency is obtained by dividing the charge capacity by the discharge capacity.

[0030] Experimental conclusion: AsFigure 4 As shown, the first charge-discharge voltage curves of the samples of Example 1 and Comparative Example 1 at room temperature in the voltage range of 2 - 4V and at a rate of 0.1C. Specifically, the first discharge specific capacity of Example 1 in the voltage range of 2 - 4V and at a rate of 0.1C is 116.3 mAh / g, and the first discharge specific capacity of Comparative Example 1 in the voltage range of 2 - 4V and at a rate of 0.1C is 98.7 mAh / g. It can be seen that the sample disclosed in Example 1 of the present invention has a more excellent first discharge specific capacity compared to the sample prepared in Comparative Example 1.

[0031] To verify the cycle performance of the present invention, the cycle performance tests of Example 1 and Comparative Example 1 were also carried out at room temperature, that is, after cycling 100 times at a rate of 0.1C, electrochemical tests were carried out again (the test steps are the same as the electrochemical test of the first discharge specific capacity), as Figure 5 shown, the discharge specific capacity of the NaNi 0.5 Mn 0.5 O2 cathode material prepared in Example 1 is 41 mAh / g, and the discharge specific capacity of Comparative Example 1 is 37 mAh / g, indicating that the performance shown by Example 1 disclosed in the present invention is more excellent compared to Comparative Example 1 after cycling 100 times.

[0032] As Figures 6 - 7 shown, Figure 6 is the CV diagram of Comparative Example 1 in the present invention, Figure 7 and is the CV diagram of Example 1, showing the cyclic voltammograms of the samples of Comparative Example 1 and Example 1 at a scanning rate of 0.1 mV / s in the voltage range of 2 - 4V, indicating that in the cathodic scan, there are four groups of reduction peaks at 2.41V, 3.21V, 3.45V and 3.6V, further indicating the sodium deintercalation / insertion ability of the present invention compared with the prior art. The redox peaks in this example correspond to the plateaus in the charge-discharge curves. The area reduction of Comparative Example 1 is relatively serious, and the reason for the area reduction is the increase in the capacity attenuation value. ΔV (i.e., the abscissa difference) can represent the polarization magnitude of the material to a certain extent. In Figure 6 , the four groups of redox reaction pairs are located at 2.91 / 2.48V, 3.36 / 3.01V, 3.59 / 3.35V and 3.79 / 3.52V respectively, and the ΔV values are 0.44V, 0.35V, 0.24 and 0.27V respectively. In Figure 7The four groups of redox reactions in Example 1 are located at 2.88 / 2.45 V, 3.28 / 3.18 V, 3.51 / 3.48 V, and 3.73 / 3.65 V respectively, and the ΔV values are 0.43 V, 0.1 V, 0.03 V, and 0.08 V respectively. The results show that the polarization of the cathode material in this Example 1 is greatly reduced, and the charge-discharge reversibility is improved. The product disclosed by the present invention can effectively inhibit the increase in resistance inside the cathode of the coating material, and can effectively protect the matrix material from side reactions and structural damage of the electrolyte.

[0033] Combining all the above embodiments, in the present invention, the O3-type NaNi 0.5 Mn 0.5 O2 sodium-ion battery cathode material coated with high-entropy oxide is prepared by the coprecipitation method. Through the verification of its physical characterization and electrochemical properties, it is shown that the O3-type NaNi 0.5 Mn 0.5 O2 prepared by the coprecipitation method disclosed by the present invention can improve the rate performance and cycling performance of O3-type NaNi 0.5 Mn 0.5 O2 by the conductivity and structural stability of the high-entropy oxide Ni-MOFs itself without affecting the crystal structure of the matrix material, effectively improving the cycle life and stability of the sodium-ion battery.

[0034] The above are only the preferred embodiments of the present invention, and do not limit the patent scope of the present invention. All equivalent structural transformations made under the inventive concept of the present invention by using the content of the specification and drawings of the present invention, or directly / indirectly applied in other related technical fields are included in the patent protection scope of the present invention.

Claims

1. A preparation method of a coated and modified NaNi 0.5 Mn 0.5 O2 cathode material, characterized in that It includes the following steps: Prepare the precursor Ni-MOFs solution. By the solvothermal method, add DMF to PTA in proportion to obtain the first mixture, and then add DMF to Ni(NO)3·6H2O in proportion to prepare the second mixture. After mixing the first mixture and the second mixture, heat them to obtain the precursor Ni-MOFs solution; Prepare the precursor Ni-MOFs. Centrifuge the cooled precursor Ni-MOFs solution at 8500 rmp for 3 - 5 min, and wash it alternately with absolute ethanol and deionized water. After centrifuging 3 - 5 times, transfer it to a drying oven at 83 - 85 °C and dry it for 5 - 7 h to obtain the precursor Ni-MOFs; Preparation of O3-type NaNi 0.5 Mn 0.5 O2. Weigh the reagents Na2CO3, NiO, and MnO2 in proportion. After mixing the three reagents, transfer them to a ball mill for sufficient grinding, and then transfer them to a tube furnace. Heat it at a heating rate of 5 °C / min to 500 °C and keep it for 12 h. After 12 h, continue to heat it to 900 °C at the same heating rate and keep it for 12 h to obtain O3-type NaNi 0.5 Mn 0.5 O2; Preparation of coated and modified NaNi 0.5 Mn 0.5 O2, mixing oxalic acid and the prepared O3-type NaNi 0.5 Mn 0.5 O2 in deionized water by stirring to obtain a third mixed solution, then adding the precursor Ni-MOFs to the third mixed solution, heating and evaporating the third mixed solution to obtain a paste material, drying the paste material and calcining it for 24 h to obtain the coated and modified NaNi 0.5 Mn 0.5 O2.

2. The preparation method of the coated and modified NaNi 0.5 Mn 0.5 O2 cathode material, characterized in that, The step of preparing the precursor Ni-MOFs solution, by the solvothermal method, adding DMF to PTA in proportion to obtain the first mixture, and then adding DMF to Ni(NO)3·6H2O in proportion to prepare the second mixture, and after mixing the first mixture and the second mixture, heating them to obtain the precursor Ni-MOFs solution, further includes: Stir the first mixture and the second mixture for 5 min respectively to fully dissolve the solutes in the first mixture and the second mixture; Mix the first mixture and the second mixture and continuously stir at 350 rmp for 30 min to obtain a turquoise transparent solution; Transfer the turquoise transparent solution into a reaction kettle, and heat the reaction kettle to 120 °C and continuously react for 12 h; After the reaction is completed, remove the reaction kettle and naturally cool it to room temperature to obtain the precursor Ni-MOFs solution.

3. The preparation method of the coated and modified NaNi 0.5 Mn 0.5 O2 cathode material, characterized in that The step of preparing the coated and modified NaNi 0.5 Mn 0.5 O2, mixing oxalic acid and the prepared O3-type NaNi 0.5 Mn 0.5 O2 in deionized water to obtain a third mixed solution, then adding the precursor Ni-MOFs to the third mixed solution, heating and evaporating the third mixed solution to obtain a paste material, drying the paste material and then calcining it for 24 h to obtain the coated and modified NaNi 0.5 Mn 0.5 O2 includes: Preparation of coated and modified NaNi 0.5 Mn 0.5 O2, oxalic acid and the prepared O3-type NaNi 0.5 Mn 0.5 O2 are stirred and mixed in deionized water to obtain a third mixed solution; Then add the precursor Ni-MOFs to the third mixture, and transfer the third mixture incorporated with the precursor Ni-MOFs into an oil bath at 80 °C and stir and evaporate to obtain a paste-like material; The paste material was placed in a vacuum oven and dried at 80 °C for 6 h to obtain a brown powder. Then, the brown powder was calcined in a tube furnace at 900 °C for 24 h to obtain coated and modified NaNi 0.5 Mn 0.5 O2.

4. The preparation method of the coated and modified NaNi 0.5 Mn 0.5 O2 cathode material, characterized in that The oxalic acid and NaNi 0.5 Mn 0.5 The mass fraction ratio of O2 is 1.5:

1.

5. A coated and modified NaNi 0.5 Mn 0.5 O2 cathode material, characterized in that The coated and modified NaNi 0.5 Mn 0.5 O2 cathode material is prepared by the preparation method of the coated and modified NaNi 0.5 Mn 0.5 O2 cathode material according to any one of claims 1 to 4.

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