A Coating Method for Lithium Nickel Cobalt Manganese Oxide Cathode Material

Abstract

The present invention discloses a coating method for lithium nickel cobalt manganese oxide cathode material, which relates to the technical field of synthesis of cathode materials. The present invention provides a coating method for lithium nickel cobalt manganese oxide cathode material, comprising the following steps: (1) mixing the lithium nickel cobalt manganese oxide cathode material and a potassium permanganate solution, and introducing an olefin; (2) drying and calcining after the reaction is completed to obtain a lithium nickel cobalt manganese oxide cathode material coated with manganese dioxide; wherein, the number of carbon atoms in the olefin ≤ 10, and the number of carbon-carbon double bonds in the olefin = 1. The present invention provides a coating method for lithium nickel cobalt manganese oxide cathode material. By mixing the lithium nickel cobalt manganese oxide cathode material and a potassium permanganate solution and introducing an olefin, the directional coating of surface defects is realized, and it is not necessary to generate an overly thick coating layer to well prevent side reactions between the electrolyte and the cathode material through the surface defects.

Description

Technical Field

[0001] The present invention relates to the technical field of cathode material synthesis, and in particular to a coating method for lithium nickel cobalt manganese oxide cathode material. Background Art

[0002] For lithium nickel cobalt manganese oxide cathode materials, especially ultra-high nickel cathode materials with Ni content exceeding 90%, residual lithium problems are likely to occur on the surface. The surface residual lithium mainly refers to substances such as LiOH and Li 2 CO 3 and the like. On the one hand, the source is that the unreacted Li in the sintering reaction remains on the surface or the surface residual lithium is generated due to the decomposition of the material during high-temperature sintering; on the other hand, it is generated when the material is placed in the air for a long time. The higher the Ni content, the more stringent the sintering conditions, and it is more difficult to sinter into a material with a specific lithium metal ratio, resulting in more surface residual lithium in the sintered product. In addition, the higher the Ni content, the more easily Li + reacts with water and CO in the air 2 to generate LiOH and Li 2 CO 3 , resulting in high surface residual lithium. As the Ni content increases, manganese in the lithium nickel cobalt manganese oxide cathode material is easily dissolved out during the cycling process and will precipitate on the negative electrode to damage the negative electrode SEI film. Mn 3+ will undergo a disproportionation reaction during the cycling process to form Mn 4+ and Mn 2+ , resulting in the fragmentation of the cathode particles and further affecting the cycling performance of the cathode material. Some surface defects such as depressions and fractures are inevitably formed on the surface of the cathode material, and these surface defects will promote the side reaction between the cathode material and the electrolyte.

[0003] By forming a coating layer on the surface of the cathode material, some surface defects can be repaired and the side reaction between the cathode material and the electrolyte can be alleviated. However, there are some problems with conventional coating methods. The conventional coating method randomly forms some coating regions on the surface of the material, and it is difficult to obtain its uniformity. The coating agent is less, which may result in some regions, especially the surface defect regions, not being coated, and the electrolyte can react with the cathode material through these surface defect regions; if the amount of the coating agent used is increased, it may lead to over-thick local coating, reducing the specific capacity and possibly increasing the impedance at the same time. Summary of the Invention

[0004] Based on this, the object of the present invention is to overcome the deficiencies of the above-mentioned prior art and provide a coating method for lithium nickel cobalt manganese oxide cathode material. The present invention provides a coating method for lithium nickel cobalt manganese oxide cathode material, which realizes the directional coating of surface defects by mixing the lithium nickel cobalt manganese oxide cathode material and potassium permanganate solution and introducing olefins, and does not need to generate a too thick coating layer to well prevent the side reaction between the electrolyte and the cathode material through the surface defects.

[0005] To achieve the above object, the technical solution adopted by the present invention is: a coating method for lithium nickel cobalt manganese oxide cathode material, comprising the following steps:

[0006] (1) Mix the lithium nickel cobalt manganese oxide cathode material and potassium permanganate solution, and introduce olefins;

[0007] (2) After the reaction is completed, dry and calcine to obtain the lithium nickel cobalt manganese oxide cathode material coated with manganese dioxide;

[0008] Among them, the number of carbon atoms in the olefin ≤ 10, and the number of carbon-carbon double bonds in the olefin = 1.

[0009] In the present invention, by mixing the lithium nickel cobalt manganese oxide cathode material and potassium permanganate solution and introducing olefins, by introducing olefins into the mixture of the lithium nickel cobalt manganese oxide cathode material and potassium permanganate solution, it is easier to adhere to the surface defect areas (pits, cracks, etc.) on the surface of the cathode material, and the attached gas can react with potassium permanganate in the solution in the defect area to form MnO 2 precipitate to make up for the defects, so as to realize the directional coating of surface defects. Without generating a too thick coating layer, it can well prevent the side reaction between the electrolyte and the cathode material through the surface defects. At the same time, the olefin gas reacts with the potassium permanganate solution to form a precipitate, and the precipitate particles are small and the coating is more uniform. Coating MnO 2 at the surface defects can form a MnO 2 rich layer inside and outside the surface of the cathode material, which can inhibit the dissolution of MnO 2 in the cathode material and the disproportionation reaction of Mn 3+ . The by-products generated by the reaction (such as alcohols) can be dissolved in the solution and removed, and the unreacted gas is removed during the drying stage, so that it will not react with the material and cause the reduction of the cathode material.

[0010] Furthermore, the present invention can also adopt the method of soaking the cathode material in a reducing gas. Place the cathode material in a high-pressure olefin environment, so that the olefin enters the inside of the cathode material through the surface defects, mix the cathode material with the potassium permanganate solution, and the olefin gas gradually overflows in the solution. The olefin reacts with potassium permanganate to generate manganese dioxide and precipitates at the surface defects.

[0011] Preferably, the olefin is at least one of ethylene and propylene; more preferably, the olefin is ethylene.

[0012] Preferably, in the step (1), the mass concentration of the potassium permanganate solution is 0.5%-5%, the pH value of the potassium permanganate solution is 7-12, and the temperature of the mixing reaction is 10-50°C; more preferably, the mass concentration of the potassium permanganate solution is 0.5%-2%, and the temperature of the mixing reaction is 10-25°C.

[0013] The inventors found that within the above mass concentration of the potassium permanganate solution and reaction temperature range, the reaction rate is slower, which can reduce the loss before the bubbles reach the surface defects.

[0014] Preferably, in the step (1), the method of introducing the olefin is: introducing the olefin in batches, using an air pump to introduce the olefin when introducing the olefin, and the air pipe of the air pump is equipped with a filter element.

[0015] Preferably, the number of times of introducing the olefin is 3-10 times, and the volume ratio of the total volume of the introduced olefin to the volume of the potassium permanganate solution is olefin: potassium permanganate solution = (0.3-1):1. More preferably, the number of times of introducing the olefin is 3-5 times, and the volume ratio of the total volume of the introduced olefin to the volume of the potassium permanganate solution is olefin: potassium permanganate solution = (0.3-0.5):1.

[0016] After a large number of experimental explorations, the inventors found that by limiting the number of times of introducing the olefin and the amount of the introduced olefin, the reaction can be controlled more completely, and finally the coating effect is better.

[0017] Preferably, the pressure of the air pump is 0.013-0.020 MPa, and the pore diameter of the filter element is 0.2-0.5 μm.

[0018] After a large number of experimental explorations, the inventors found that the pore diameter of the filter element is the main factor affecting the bubble size of the introduced gas. When the pore diameter of the filter element is 0.2-0.5 μm, the bubble size of the introduced gas is appropriate, and the coating effect is better.

[0019] Preferably, in the step (2), the drying temperature is 60-80°C, and the drying time is 8-12 h; the calcination temperature is 450-550°C, and the calcination time is 6-8 h.

[0020] In addition, the present invention provides a lithium nickel cobalt manganese oxide cathode material obtained by the coating method of the above lithium nickel cobalt manganese oxide cathode material.

[0021] Furthermore, the present invention provides the application of the lithium nickel cobalt manganese oxide cathode material in the preparation of a lithium ion battery.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows: By mixing the lithium nickel cobalt manganese oxide cathode material with a potassium permanganate solution and introducing an olefin, that is, by introducing an olefin into the mixture of the lithium nickel cobalt manganese oxide cathode material and the potassium permanganate solution, it is easier to adhere to the surface defect areas (such as pits, cracks, etc.) of the cathode material. The attached gas can react with the potassium permanganate in the solution in the defect area to form MnO 2 precipitate to make up for the defects, so as to achieve directional coating of the surface defects. Without generating an overly thick coating layer, it can well prevent side reactions between the electrolyte and the cathode material through the surface defects. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a diagram of the lithium nickel cobalt manganese oxide cathode material coated with manganese dioxide prepared in Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0024] To better illustrate the purpose, technical solution and advantages of the present invention, the present invention will be further described below in conjunction with the drawings and specific embodiments.

[0025] In the embodiments, the experimental methods used are all conventional methods without special instructions, and the materials, reagents, etc. used can be obtained from commercial channels without special instructions.

[0026] Examples 1-6 and Comparative Examples 1-2

[0027] Example 1

[0028] This example provides a coating method for a lithium nickel cobalt manganese oxide cathode material. The olefin used in the present invention is ethylene, and the method includes the following steps:

[0029] (1) Mix 500 g of lithium nickel cobalt manganese oxide cathode material (LiNi 0.9 Co 0.05 Mn 0.05 O 2 ) and a potassium permanganate solution, and introduce the olefin in batches. When introducing ethylene, it is introduced by an air pump, and the air delivery pipe of the air pump is equipped with a filter element (PE filter element);

[0030] Among them, the mass concentration of the potassium permanganate solution is 0.5%, the pH is 8, and the temperature of the mixing reaction is 20°C; the number of times of introducing ethylene is 5 times, and the volume of olefin introduced each time is 100 cm 3 , and the volume ratio of the total volume of introduced ethylene to the volume of the potassium permanganate solution is ethylene: potassium permanganate solution = 0.5:1. Specifically, the total volume of ethylene used is 500 cm 3 , and the volume of the potassium permanganate solution is 1 L; the pressure of the air pump is 0.018 MPa, and the pore diameter of the filter element is 0.45 μm;

[0031] (2) After the reaction is completed, it is dried and calcined to obtain a lithium nickel cobalt manganese oxide cathode material coated with manganese dioxide;

[0032] Among them, the drying temperature is 70 °C and the drying time is 10 h; the calcination temperature is 450 °C and the calcination time is 8 h.

[0033] Example 2

[0034] This example provides a coating method for a lithium nickel cobalt manganese oxide cathode material. The only difference between this example and Example 1 is that in step (1), the olefin used in the present invention is propylene; among them, the mass concentration of the potassium permanganate solution is 0.5%, the pH is 8, the temperature of the mixed reaction is 20 °C; the number of times of introducing propylene is 5 times, and the volume of olefin introduced each time is 100 cm 3 , the volume ratio of the total volume of propylene introduced to the volume of the potassium permanganate solution is propylene: potassium permanganate solution = 0.5:1. Specifically, the total volume of propylene used is 500 cm 3 , the volume of the potassium permanganate solution is 1 L; the pressure of the air pump is 0.018 MPa, and the pore size of the filter element is 0.45 μm.

[0035] Example 3

[0036] This example provides a coating method for a lithium nickel cobalt manganese oxide cathode material. The only difference between this example and Example 1 is that in step (2), the calcination temperature is 550 °C and the calcination time is 6 h.

[0037] Example 4

[0038] This example provides a coating method for a lithium nickel cobalt manganese oxide cathode material. The only difference between this example and Example 1 is that in step (1), the number of times of introducing ethylene is 3 times, and the volume of olefin introduced each time is 100 cm 3 , the volume ratio of the total volume of ethylene introduced to the volume of the potassium permanganate solution is ethylene: potassium permanganate solution = 0.3:1. Specifically, the total volume of ethylene used is 300 cm 3 , the volume of the potassium permanganate solution is 1 L.

[0039] Example 5

[0040] This example provides a coating method for a lithium nickel cobalt manganese oxide cathode material. The only difference between this example and Example 1 is that in step (1), when introducing olefin in batches, an air pump is used, and the air delivery pipe of the air pump is not equipped with a filter element.

[0041] Example 6

[0042] This embodiment provides a coating method for lithium nickel cobalt manganese oxide cathode material. The only difference between this embodiment and Embodiment 1 is that in step (1), the mass concentration of the potassium permanganate solution is 5%, the pH is 8, and the temperature of the mixing reaction is 50°C; the number of times of ethylene introduction is 5 times, and the volume of olefin introduced each time is 200 cm 3 , and the volume ratio of the total volume of ethylene introduced to the volume of the potassium permanganate solution is ethylene: potassium permanganate solution 1:1. Specifically, the total volume of ethylene used is 1000 cm 3 , and the volume of the potassium permanganate solution is 1 L; the pressure of the air pump is 0.018 MPa, and the pore diameter of the filter element is 0.45 μm.

[0043] Comparative Example 1

[0044] In this comparative example, potassium permanganate coating layer was prepared using carbon-coated lithium nickel cobalt manganese oxide. The preparation method is as follows: Take 500 g of LiNi coated with C on the surface 0.9 Co 0.05 Mn 0.05 O 2 , and place it in 1 L of a neutral potassium permanganate solution with a mass fraction of 0.5% and a temperature of 20°C, so that the potassium permanganate solution completely submerges the cathode material. After the reaction is completed, separate the cathode material from the solution, place the cathode material in an oven, dry it at 70°C for 10 h, and then calcine it in a muffle furnace at 450°C for 8 h.

[0045] Comparative Example 2

[0046] In this comparative example, a manganese dioxide coating layer was prepared using the common precipitation method. The preparation method is as follows: Take 500 g of LiNi 0.9 Co 0.05 Mn 0.05 O 2 , and place it in 1 L of a neutral potassium permanganate solution with a mass fraction of 0.5% and a temperature of 20°C, so that the potassium permanganate solution completely submerges the cathode material. Then add 5 g of manganese hydroxide to the solution to dissolve it. After precipitation, separate the cathode material from the solution, place the cathode material in an oven, dry it at 70°C for 10 h, and then calcine it in a muffle furnace at 450°C for 8 h.

[0047] Performance Test

[0048] Test procedure: The cathode materials obtained from the examples and comparative examples were formulated into coin cells for testing the electrochemical performance of lithium-ion batteries. The specific steps were as follows: Using N-methylpyrrolidone as the solvent, the cathode active material was uniformly mixed with acetylene black and PVDF in a mass ratio of 9.2:0.5:0.3, coated on aluminum foil, dried in a blast oven at 80 °C for 8 h, and then vacuum dried at 120 °C for 12 h. The battery was assembled in a glove box under argon protection. The negative electrode was a lithium metal sheet, the separator was a polypropylene membrane, and the electrolyte was 1 M LiPF6-EC / DMC (1:1, v / v). A 2032-type coin cell case was used to assemble a coin cell in a glove box under argon protection, and then the electrochemical performance was tested at 3.0 - 4.5 V at 25 °C.

[0049] Test results: As shown in Table 1 below.

[0050] Table 1

[0051]

[0052] Figure 1 Figure is for the lithium nickel cobalt manganese oxide cathode material coated with manganese dioxide prepared in Example 1, and Table 1 shows the electrochemical performance test results. When the lithium nickel cobalt manganese oxide cathode material coated with manganese dioxide prepared in the examples of the present invention is applied to a coin cell, the discharge capacity at 0.1C is above 200 mAh / g, the discharge specific capacity after 100 cycles is 180 mAh / g, and the cycle retention rate reaches over 88%.

[0053] Among them, in Example 5, without a filter element, the bubbles were larger and more difficult to adhere, the coating amount decreased, and the cycle performance decreased slightly. In Example 6, the temperature of the mixed reaction and the mass concentration of the potassium permanganate solution were too high, the reaction was too fast, and many ethylene bubbles reacted before reaching the particle surface, so a lot of manganese dioxide precipitates were formed. Even if the amount of inlet ethylene was increased, the coating effect was still inferior to that of Example 1.

[0054] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present invention and not to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for coating a lithium nickel cobalt manganese oxide cathode material, characterized in that, it includes the following steps: (1) Mix the lithium nickel cobalt manganese oxide cathode material with a potassium permanganate solution and introduce an olefin; (2) After the reaction is completed, dry and calcine to obtain a lithium nickel cobalt manganese oxide cathode material coated with manganese dioxide; wherein, the number of carbon atoms in the olefin ≤ 10, and the number of carbon-carbon double bonds in the olefin = 1.

2. The method for coating a lithium nickel cobalt manganese oxide cathode material according to claim 1, characterized in that, the olefin is at least one of ethylene and propylene.

3. The method for coating a lithium nickel cobalt manganese oxide cathode material according to claim 2, characterized in that, the olefin is ethylene.

4. The method for coating a lithium nickel cobalt manganese oxide cathode material according to claim 1, characterized in that, in the step (1), the mass concentration of the potassium permanganate solution is 0.5% - 5%, and the temperature of the mixing reaction is 10 - 50 °C.

5. The method for coating a lithium nickel cobalt manganese oxide cathode material according to claim 4, characterized in that, the mass concentration of the potassium permanganate solution is 0.5% - 2%, and the temperature of the mixing reaction is 10 - 25 °C.

6. The method for coating a lithium nickel cobalt manganese oxide cathode material according to claim 1, characterized in that, in the step (1), the method for introducing the olefin is: introduce the olefin in batches, use an air pump to introduce the olefin when introducing the olefin, and the air pipe of the air pump is equipped with a filter element.

7. The method for coating a lithium nickel cobalt manganese oxide cathode material according to claim 6, characterized in that, the number of times of introducing the olefin is 3 - 10 times, and the volume ratio of the total volume of the introduced olefin to the volume of the potassium permanganate solution is olefin: potassium permanganate solution = (0.3 - 1):

1.

8. The method for coating a lithium nickel cobalt manganese oxide cathode material according to claim 7, characterized in that, the number of times of introducing the olefin is 3 - 5 times, and the volume ratio of the total volume of the introduced olefin to the volume of the potassium permanganate solution is olefin: potassium permanganate solution = (0.3 - 0.5):

1.

9. The method for coating a lithium nickel cobalt manganese oxide cathode material according to claim 6, characterized in that, the pressure of the air pump is 0.013 - 0.020 MPa, and the pore size of the filter element is 0.2 - 0.5 μm.

10. The method for coating a lithium nickel cobalt manganese oxide cathode material according to claim 1, characterized in that, in the step (2), the drying temperature is 60 - 80 °C, and the drying time is 8 - 12 h; the calcination temperature is 450 - 550 °C, and the calcination time is 6 - 8 h.

11. A lithium nickel cobalt manganese oxide cathode material obtained by using the method for coating a lithium nickel cobalt manganese oxide cathode material according to claim 1.

12. An application of the lithium nickel cobalt manganese oxide cathode material according to claim 11 in the preparation of a lithium-ion battery.

Images