Method for removing residual alkali on surface of high-nickel ternary positive electrode material, positive electrode material and lithium ion battery

Abstract

The invention discloses a method for removing residual alkali on the surface of a high-nickel ternary positive electrode material, the positive electrode material and a lithium ion battery, and the method comprises the following steps: 1) adding a lithium salt into a green organic solvent, mixing, and stirring until the mixture is clear and free of precipitate to prepare a lithium salt solution; (2) adding the air failure high-nickel ternary positive electrode material into the lithium salt solution, stirring and drying to obtain powder; and (3) carrying out centrifugal washing, drying and sintering on the powder to obtain the repaired high-nickel ternary positive electrode material. According to the method, the air-failure high-nickel ternary positive electrode material is reacted in the lithium salt solution, so that residual alkali on the surface of the positive electrode material is effectively removed, and meanwhile, a stable rapid lithium guide modification layer is formed on the surface of the positive electrode material. Compared with the prior art, the method is simple and convenient to operate and short in technological process, and the stability of the high-nickel ternary positive electrode material in the air is remarkably improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium ion battery positive electrode materials, and in particular relates to a method for removing residual alkali on the surface of a high-nickel ternary positive electrode material, a positive electrode material and a lithium ion battery. Background Art

[0002] Against the backdrop of increasing fossil fuel consumption, lithium-ion batteries, as a clean energy source used in portable electronic devices, have become an indispensable part of human life. With the growing demand for portable energy storage devices, long-distance electric vehicles, and hybrid electric vehicles, the development of cathode materials with high capacity and high voltage has become particularly important. Therefore, a key direction in lithium-ion battery research is the development of cathode materials that combine high energy density with excellent stability at a reasonable cost. High-nickel ternary cathode materials have attracted much attention due to their high theoretical capacity and relatively low nickel cost.

[0003] High nickel content can improve the energy density of ternary materials, but it will also affect their industrialization. During the synthesis process of high-nickel ternary positive electrode materials, it is usually necessary to add excess lithium precursors to compensate for the lithium loss during high-temperature calcination and suppress cation disorder in the crystal structure. However, this will cause residual lithium compounds (such as LiOH, Li2CO3) to exist on the surface of the material. Lithium compounds have an electrochemical passivation effect, which seriously affects the lithium conduction kinetics on the surface of the positive electrode material, resulting in failure of the positive electrode material. The synthesis process of high-nickel ternary materials is not the only source of lithium compounds. Compared with other positive electrode materials, high-nickel ternary materials are extremely sensitive to ambient air. During long-term storage or transportation, surface alkaline substances are easily generated, resulting in a decrease in electrochemical performance and material failure. In addition, during the preparation of the positive electrode sheet, the alkaline product increases the pH of the slurry, causing gelation and making slurrying difficult, resulting in a significant decrease in the processing performance of the positive electrode sheet.

[0004] Water washing is commonly used to remove residual alkali from the surface of high-nickel ternary cathode materials. However, this process can easily lead to the dissolution of lattice lithium, destroying the material structure. Currently, the main methods for removing residual alkali from the surface of high-nickel ternary cathode materials are to dope the bulk phase of the material to stabilize the structure and to stabilize the interface through surface modification.

[0005] Currently, researchers are using the following main technologies to remove residual alkali from the surface of high-nickel ternary cathode materials. For example, patent CN113666431A discloses a method for removing residual alkali from high-nickel ternary cathode materials. This method uses a solvent to ultrasonically clean the high-nickel ternary cathode material, followed by spray drying the washed system to obtain the de-alkalied high-nickel ternary cathode material. This method is simple to operate, thoroughly removes residual alkali from the high-nickel ternary cathode material, and reduces washing time. However, the washing process still damages the material's surface structure. CN116072876A discloses a high-nickel ternary cathode material and a method for removing residual alkali from its surface. This method involves mixing a primary sintered material containing a precursor and a lithium source with an organic solvent, separating the solid and liquid, and drying the solid phase. The dried material is then mixed with a coating material and subjected to a secondary sintering process to form a coating layer on the material surface. This method simultaneously removes alkali and forms a coating layer on the material surface, improving the material's electrochemical performance. However, it requires multiple high-temperature sintering processes, which results in high energy consumption and environmental pollution. CN115332471A discloses a method for removing residual alkali and coating a high-nickel ternary cathode material. This method uses the strong oxidizing properties of ozone to oxidize residual lithium into lithium peroxide. This is then reacted with titanium tetrachloride to form lithium titanate, which neutralizes the residual lithium on the surface. The titanium tetrachloride is then vapor-deposited with oxygen to form a titanium dioxide coating. This method uses vapor deposition to treat the material and form the coating. However, this method requires not only controlling the amount of reactant gas but also the pressure in the equipment.

[0006] Therefore, there is an urgent need for a method to remove residual alkali on the surface of the material with low cost, simple operation and low energy consumption without destroying the structure of the high-nickel ternary positive electrode material. Summary of the Invention

[0007] To solve the above problems, the present invention proposes a method for removing residual alkali on the surface of high-nickel ternary positive electrode materials, a positive electrode material, and a lithium-ion battery. The method of the present invention converts the residual alkali on the surface of the failed high-nickel ternary positive electrode material into a stable fast-lithium-conducting modification layer, which not only significantly reduces the residual alkali content on the surface of the material, but also effectively solves the problem of instability of the high-nickel material in the air. In addition, the method converts the surface residual alkali into a fast-lithium-conducting modification layer, further improving the electrochemical performance and structural stability of the high-nickel ternary positive electrode material. At the same time, the present invention has the advantages of low cost, simple operation, and low energy consumption.

[0008] The technical solution adopted in the present invention is as follows:

[0009] A method for removing residual alkali on the surface of a high-nickel ternary positive electrode material comprises the following steps:

[0010] (1) adding lithium salt to a green organic solvent and mixing and stirring to prepare a lithium salt solution;

[0011] (2) adding the air-depleted high-nickel ternary cathode material to the lithium salt solution, stirring and drying to obtain a powder;

[0012] (3) The powder is centrifugally washed, dried, and sintered to obtain a repaired high-nickel ternary positive electrode material.

[0013] Furthermore, the lithium salt is one or more of lithium difluorophosphate, lithium hexafluorophosphate, lithium trifluorophosphate, and lithium monofluorophosphate.

[0014] Furthermore, in step (1), the green organic solvent is one or more of ethanol, methanol, ethylene glycol, propylene glycol, and isopropanol, preferably ethanol.

[0015] Furthermore, the mass fraction of lithium salt in the lithium salt solution is 1% to 5%.

[0016] Furthermore, the high-nickel ternary positive electrode material is a nickel-cobalt-manganese ternary positive electrode material or a nickel-cobalt-aluminum ternary positive electrode material.

[0017] Furthermore, in step (2), the mass ratio of the high-nickel ternary positive electrode material to the lithium salt solution is 1:10 to 50.

[0018] Furthermore, the stirring time in step (1) is 2 to 6 hours, and the stirring speed is 200-1000 r / min; the stirring time in step (2) is 5 to 48 hours, and the stirring speed is not less than 400 r / min.

[0019] Furthermore, in step (3), the washing is carried out using one or more of ethanol, methanol, ethylene glycol, propylene glycol, and isopropanol; the sintering temperature is 500-1000° C., and the sintering time is 5-12 hours.

[0020] A high-nickel ternary positive electrode material is prepared using the above method.

[0021] A lithium ion battery, wherein the positive electrode material of the lithium ion battery is prepared by the above method.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] (1) The method of the present invention uses a specific lithium salt to react with the residual alkali on the surface of the high-nickel ternary positive electrode material under certain conditions, thereby effectively removing the residual alkali on the surface of the positive electrode material. The residual alkali on the surface of the positive electrode material is removed by reacting the lithium salt with lithium hydroxide or lithium carbonate.

[0024] (2) The present invention not only reduces the residual alkali on the surface of the cathode material, but also converts the residual alkali in situ into a stable rapid lithium-conducting interface layer. Compared with commercial ternary cathode materials, the repaired ternary cathode material exhibits higher air stability and enhanced electrochemical performance due to the presence of the rapid lithium-conducting interface layer.

[0025] (3) The raw materials used in the residual alkali removal process of the present invention are inexpensive, providing an economically feasible solution for large-scale production. The equipment requirements are low, and the process conditions are easy to implement, making it suitable for large-scale production applications. The process has the advantages of being easy to operate, fast and efficient, and having low energy consumption, which is conducive to future large-scale applications.

[0026] (4) The process for removing residual alkali of the present invention is green and environmentally friendly. It does not use any acid, alkali or toxic solvent. The reaction can be completed at room temperature in an open environment using green solvents, and no secondary pollution such as any toxic byproducts is generated. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 Schematic diagram of the repaired high-nickel ternary positive electrode material in an embodiment of the present invention.

[0028] Figure 2 The high nickel ternary positive electrode material (LiNi 0.82 Co 0.15 Mn 0.03 O2); among them, (a) is the scanning electron microscope image of the repaired high-nickel ternary positive electrode material; (b) is the P element distribution map; (c) is the F element distribution map.

[0029] Figure 3 The high nickel ternary positive electrode material (LiNi 0.82 Co 0.15 Mn 0.03 (a) is the X-ray photoelectron spectrum of P 2p; (b) is the X-ray photoelectron spectrum of F1s.

[0030] Figure 4 The high nickel ternary positive electrode material (LiNi 0.82 Co 0.15 Mn 0.03 O2) surface residual alkali content diagram.

[0031] Figure 5 The high nickel ternary positive electrode material (LiNi 0.82 Co 0.15 Mn 0.03 O2) X-ray diffraction pattern.

[0032] Figure 6 The high nickel ternary positive electrode material (LiNi 0.82 Co 0.15 Mn 0.03 Raman spectrum of O2).

[0033] Figure 7 The high nickel ternary positive electrode material (LiNi 0.82 Co 0.15 Mn 0.03 Infrared spectrum of O2).

[0034] Figure 8 The high nickel ternary positive electrode material (LiNi 0.82 Co 0.15 Mn 0.03 O2) thermogravimetric-differential scanning calorimetry diagram.

[0035] Figure 9 The high nickel ternary positive electrode material (LiNi 0.82 Co 0.15 Mn 0.03 O2) on the cycling performance of lithium batteries.

[0036] Figure 10 The high nickel ternary positive electrode material (LiNi 0.82 Co 0.15 Mn 0.03 O2) on the rate performance of lithium batteries.

[0037] Figure 11 The high nickel ternary positive electrode material (LiNi 0.82 Co 0.15 Mn 0.03 O2) on the cycling performance of graphite full battery. DETAILED DESCRIPTION

[0038] The technical solution of the present invention will be further described in detail below with reference to specific examples and accompanying drawings.

[0039] A method for removing residual alkali on the surface of a high-nickel ternary positive electrode material comprises the following steps:

[0040] (1) adding a lithium salt to a green organic solvent, mixing, and stirring at room temperature for 2 to 6 hours at a stirring speed of 200 to 1000 r / min to prepare a lithium salt solution; the lithium salt is one or more of lithium difluorophosphate, lithium hexafluorophosphate, lithium trifluorophosphate, and lithium monofluorophosphate; the green organic solvent is one or more of ethanol, methanol, ethylene glycol, propylene glycol, and isopropanol; the mass fraction of the lithium salt in the lithium salt solution is 1% to 5%;

[0041] (2) adding an air-ineffective high-nickel ternary positive electrode material to the lithium salt solution, stirring for 5 to 48 hours at a stirring speed of not less than 400 r / min, and then drying to obtain a powder; the high-nickel ternary positive electrode material is a nickel-cobalt-manganese ternary positive electrode material or a nickel-cobalt-aluminum ternary positive electrode material; and the mass ratio of the high-nickel ternary positive electrode material to the lithium salt solution is 1:10 to 50.

[0042] This step involves placing the cathode powder in a lithium salt solution and stirring it at room temperature. This reaction involves the lithium salt reacting with lithium carbonate and lithium hydroxide, allowing the residual alkali on the surface of the high-nickel ternary cathode material to fully react.

[0043] (3) The powder is centrifuged and washed to remove residual lithium salts from the reaction through multiple washings, and then dried and sintered; the sintering temperature is 500-1000° C. and the time is 5-12 hours to obtain a repaired high-nickel ternary positive electrode material. The washing is performed using one or more of ethanol, methanol, ethylene glycol, propylene glycol, and isopropyl alcohol.

[0044] The use of a green organic solvent for washing in this step dissolves residual lithium salts from the reaction, thus preventing the residual lithium salt from affecting the positive electrode powder. Furthermore, a simple chemical reaction and sintering treatment facilitates structural repair of the material, transforming the rock salt structure into a layered structure.

[0045] Unless otherwise specified, the experimental methods used in the following examples are conventional methods, and the materials, reagents, etc. used in the examples are all commercially available unless otherwise specified.

[0046] Example 1

[0047] 1) A certain proportion of lithium difluorophosphate was added to ethanol to form a lithium difluorophosphate solution with a mass fraction of 1%, and the mixture was stirred at room temperature for 3 hours at a stirring speed of 400 r / min.

[0048] 2) Air-ineffective high nickel ternary cathode material (LiNi 0.82 Co 0.15 Mn 0.03 O2) was added to the lithium difluorophosphate solution prepared in step 1) at a mass ratio of 1:20 between the high-nickel ternary cathode material and the lithium difluorophosphate solution. The mixture was stirred at room temperature for 6 hours at a stirring speed of 500 r / min. The high-nickel ternary cathode material treated with the lithium difluorophosphate solution was then placed in a vacuum drying oven at 70°C for 10 hours to obtain a powder.

[0049] This step involves placing the high-nickel ternary cathode material in a lithium salt solution and stirring it at room temperature. This reaction involves lithium difluorophosphate reacting with lithium carbonate and lithium hydroxide, allowing the residual alkali on the surface of the high-nickel ternary cathode material to fully react.

[0050] 3) The powder obtained in step 2) was added to ethanol and centrifuged at 9000 rpm for 3 minutes. After centrifugation twice, the powder was placed in an 80°C vacuum drying oven for 12 hours. The dried powder was placed in a tube furnace under an oxygen atmosphere and sintered at a heating rate of 5°C / min to 600°C for 5 hours. After natural cooling, the repaired high-nickel ternary cathode material was obtained.

[0051] The addition of ethanol in this step dissolves any residual lithium difluorophosphate, thus preventing the resulting high-nickel ternary cathode material from being affected by residual lithium difluorophosphate. Furthermore, a simple chemical reaction and sintering treatment facilitates structural repair of the material, transforming the rock salt structure into a layered structure.

[0052] 4) Assembling the high nickel ternary positive electrode material obtained in step 3) into a lithium battery.

[0053] The schematic diagram of the repaired high nickel ternary positive electrode material in this embodiment is as follows Figure 1 shown. Figure 2 This is a scanning electron microscope image and energy spectrum analysis diagram of the high-nickel ternary positive electrode material after repair in Example 1. It can be seen from the figure that the P and F elements are evenly distributed on the surface of the high-nickel material.

[0054] like Figure 3 The figure shows the X-ray photoelectron spectrum of the high nickel ternary cathode material after repair in Example 1. As can be seen from the figure, the repaired material has peaks of Li3PO4 and LiF, which further indicates that a Li3PO4-LiF coating has formed on the surface of the material.

[0055] like Figure 4 Figure 2 shows the surface residual alkali content of the high-nickel ternary cathode material in Example 1 before and after repair. Automatic potentiometric titration revealed that the original sample had a residual alkali content of 0.106 wt% LiOH and 4.7017 wt% LiCO. The repaired sample had a residual alkali content of 0.0198 wt% LiOH and 0.1202 wt% LiCO. This indicates a significant reduction in the residual alkali content of the original sample.

[0056] like Figure 5 Shown are the X-ray diffraction patterns of the high-nickel ternary positive electrode material before and after repair in Example 1. From bottom to top, the graph shows the spectra of the lithium carbonate PDF card, the high-nickel ternary positive electrode material, and the repaired high-nickel ternary positive electrode material. As can be seen from the figure, after the residual alkali is formed on the surface of the high-nickel ternary positive electrode material, the impurity peak of lithium carbonate appears. The repaired high-nickel ternary positive electrode material has no additional impurity peaks. This indicates that the crystal phase of the repaired material has recovered.

[0057] like Figure 6The following are Raman spectra of the high nickel ternary cathode material before and after repair in Example 1. As can be seen from the figure, the peaks of LiOH and Li2CO3 weakened after repair, indicating that the residual alkali on the surface of the original sample was significantly reduced after repair.

[0058] like Figure 7 The following are infrared spectra of the high nickel ternary cathode material before and after repair in Example 1. After testing and analysis, the residual alkali absorption peak on the surface of the repaired sample was significantly weakened, indicating that the residual alkali on the surface of the repaired sample was significantly improved.

[0059] like Figure 8 Figure 2 shows thermogravimetric-differential scanning calorimetry (TG-DSC) images of the high-nickel ternary cathode material before and after repair in Example 1. Compared to the original sample, the repaired sample (mass loss due to self-decomposition at 700°C) exhibits improved mass loss at two other locations (removal of surface adsorbed impurities between 200°C and 500°C, and decomposition of surface impurities between 500°C and 700°C).

[0060] like Figure 9 The graph shows the cycle performance of the positive electrode materials before and after repair after the lithium negative electrode was assembled into a battery. The positive electrode materials were tested for cycle stability at 1C in the voltage range of 2.8 to 4.3 V at room temperature. The original electrode had a 0.2C first discharge capacity of 164.9 mAh / g. After 300 cycles, the discharge capacity dropped to 1.02 mAh / g, and the capacity retention rate was almost zero. In contrast, the repaired electrode had a 0.2C first discharge capacity of 184.4 mAh / g. After 300 cycles, the discharge capacity dropped to 95.5 mAh / g, and the capacity retention rate was 58.5%. This shows that the cycle stability of the high-nickel ternary positive electrode material obtained by the present invention is improved and the capacity is restored.

[0061] like Figure 10 The figure shows the rate performance of a battery assembled with a lithium negative electrode using the repaired and unrepaired cathode materials. As the current density of the test cell increased from 0.2C to 10C, the discharge specific capacities of the original electrode were 157.5, 116.1, 86.8, 52.2, 0.57, and 0.5 mAh / g, respectively. The discharge specific capacities of the repaired electrode were 181.9, 164.4, 146.5, 127.1, 92.5, and 45.6 mAh / g, respectively. This comparison demonstrates that the repaired electrode consistently exhibits superior cycling performance at all current densities.

[0062] like Figure 11The graph shows the cycle performance of the positive electrode materials before and after repair, after the battery was reassembled with the graphite negative electrode. The positive electrode materials were tested for cycle stability at 1C in the voltage range of 2.8 to 4.3 V at room temperature. The discharge capacity of the original electrode after 500 cycles was 22.3 mAh / g, and the capacity retention rate was 22.8%. The discharge capacity of the repaired electrode after 500 cycles was 87.3 mAh / g, and the capacity retention rate was 55.6%. This further shows that the cycle performance of the high-nickel ternary positive electrode material obtained in this application has been improved.

[0063] Example 2

[0064] 1) A certain proportion of lithium difluorophosphate was added to ethanol to form a lithium difluorophosphate solution with a mass fraction of 2%, and the mixture was stirred at room temperature for 2 hours at a stirring speed of 500 r / min.

[0065] 2) Air-ineffective high nickel ternary cathode material (LiNi 0.80 Co 0.15 Al 0.05 O2) was added to the lithium difluorophosphate solution prepared in step 1) at a mass ratio of 1:15 between the high-nickel ternary cathode material and the lithium difluorophosphate solution. The mixture was stirred at room temperature for 8 hours at a stirring speed of 450 r / min. The high-nickel ternary cathode material treated with the lithium difluorophosphate solution was then placed in a vacuum drying oven at 70°C for 12 hours to obtain a powder.

[0066] This step involves placing the high-nickel ternary cathode material in a lithium salt solution and stirring it at room temperature. This reaction involves lithium difluorophosphate reacting with lithium carbonate and lithium hydroxide, allowing the residual alkali on the surface of the high-nickel ternary cathode material to fully react.

[0067] 3) The powder obtained after the reaction treatment in step 2) was added to ethanol and centrifuged at 9000 rpm for 3 minutes. After centrifugation twice, the powder was placed in an 80°C vacuum drying oven for 10 hours. The dried positive electrode powder was placed in a tube furnace under an oxygen atmosphere and sintered at a heating rate of 5°C / min to 700°C for 8 hours. After natural cooling, the repaired high-nickel ternary positive electrode material was obtained.

[0068] The addition of ethanol in this step dissolves any residual lithium difluorophosphate, thus preventing the resulting high-nickel ternary cathode material from being affected by residual lithium difluorophosphate. Furthermore, a simple chemical reaction and sintering treatment facilitates structural repair of the material, transforming the rock salt structure into a layered structure.

[0069] 4) Assembling the high nickel ternary positive electrode material obtained in step 3) into a lithium battery.

[0070] Electrochemical tests were conducted on batteries assembled with the repaired positive electrode materials, and it was found that the initial specific capacity of the repaired batteries was nearly 30 mAh / g higher than that of the original batteries, indicating that the method of the present invention is also effective in repairing nickel-cobalt-aluminum ternary positive electrode materials.

[0071] Example 3

[0072] 1) A certain proportion of lithium hexafluorophosphate was added to ethanol to form a lithium hexafluorophosphate solution with a mass fraction of 1%, and the mixture was stirred at room temperature for 5 hours at a stirring speed of 500 r / min.

[0073] 2) Air-ineffective high nickel ternary cathode material (LiNi 0.82 Co 0.15 Mn 0.03 O2) was added to the lithium hexafluorophosphate solution prepared in step 1) at a mass ratio of 1:20 between the high-nickel ternary cathode material and the lithium hexafluorophosphate solution. The mixture was stirred at room temperature for 6 hours at a speed of 600 r / min. The high-nickel ternary cathode material treated with the lithium hexafluorophosphate solution was then placed in a vacuum drying oven at 70°C for 10 hours to obtain a powder.

[0074] This step involves placing the high-nickel ternary cathode material in a lithium salt solution and stirring it at room temperature. This reaction involves lithium hexafluorophosphate reacting with lithium carbonate and lithium hydroxide, allowing the residual alkali on the surface of the high-nickel ternary cathode material to fully react.

[0075] 3) The powder obtained after the reaction treatment in step 2) was added to ethanol and centrifuged at 9000 rpm for 3 minutes. After centrifugation twice, the powder was placed in a 90°C vacuum drying oven for 11 hours. The dried positive electrode powder was placed in a tube furnace under an oxygen atmosphere and sintered at a heating rate of 5°C / min. The sintering temperature was 650°C for 8 hours. After natural cooling, the repaired high-nickel ternary positive electrode material was obtained.

[0076] The addition of ethanol in this step dissolves any residual lithium hexafluorophosphate, thus minimizing the effects of residual lithium hexafluorophosphate on the resulting high-nickel ternary cathode material. Furthermore, a simple chemical reaction and sintering treatment facilitates structural repair of the material, transforming the rock salt structure into a layered structure.

[0077] 4) Assembling the high nickel ternary positive electrode material obtained in step 3) into a lithium battery.

[0078] Electrochemical testing of batteries assembled with the repaired cathode material revealed that the initial specific capacity of the repaired battery returned to 190 mAh / g, an increase of nearly 30 mAh / g over the original capacity. Furthermore, the crystalline phase of the repaired material also returned to normal, demonstrating that the method is effective for repairing high-nickel ternary cathode materials.

[0079] Example 4

[0080] 1) A certain proportion of lithium trifluorophosphate was added to ethanol to form a lithium trifluorophosphate solution with a mass fraction of 1%, and the mixture was stirred at room temperature for 4 hours at a stirring speed of 450 r / min.

[0081] 2) Air-ineffective high nickel ternary cathode material (LiNi 0.60 Co 0.20 Mn 0.20 O2) was added to the lithium trifluorophosphate solution prepared in step 1) at a mass ratio of 1:20 between the high-nickel ternary cathode material and the lithium trifluorophosphate solution. The mixture was stirred at room temperature for 7 hours at a speed of 500 r / min. The high-nickel ternary cathode material treated with the lithium trifluorophosphate solution was then placed in a vacuum drying oven at 80°C for 10 hours to obtain a powder.

[0082] This step involves placing the high-nickel ternary cathode material in a lithium salt solution and stirring it at room temperature. This reaction involves lithium trifluorophosphate reacting with lithium carbonate and lithium hydroxide, allowing the residual alkali on the surface of the high-nickel ternary cathode material to fully react.

[0083] 3) The powder obtained after the reaction treatment in step 2) was added to ethanol and centrifuged at 9000 rpm for 3 minutes. After centrifugation twice, the powder was placed in an 80°C vacuum drying oven for 12 hours. The dried positive electrode powder was placed in a tube furnace under an oxygen atmosphere and sintered at a heating rate of 5°C / min to 700°C for 5 hours. After natural cooling, the repaired high-nickel ternary positive electrode material was obtained.

[0084] Adding ethanol in this step dissolves residual lithium trifluorophosphate, thus preventing the resulting high-nickel ternary cathode material from being affected by residual lithium trifluorophosphate. Furthermore, a simple chemical reaction and sintering treatment facilitates structural repair of the material, transforming the rock salt structure into a layered structure.

[0085] 4) Assembling the high nickel ternary positive electrode material obtained in step 3) into a lithium battery.

[0086] Electrochemical testing of batteries assembled with the repaired cathode material revealed that the initial specific capacity of the repaired battery had returned to 180 mAh / g, an increase of nearly 20 mAh / g over the original capacity. Furthermore, the crystalline phase of the repaired material had returned to normal, demonstrating the effectiveness of the method.

[0087] Example 5

[0088] 1) A certain proportion of lithium monofluorophosphate was added to ethanol to form a lithium monofluorophosphate solution with a mass fraction of 1%, and the mixture was stirred at room temperature for 3 hours at a stirring speed of 500 r / min.

[0089] 2) Air-ineffective high nickel ternary cathode material (LiNi 0.80 Co 0.10 Mn 0.10 O2) was added to the lithium monofluorophosphate solution from step 1, with a mass ratio of the high-nickel ternary cathode material to the lithium monofluorophosphate solution of 1:20. The mixture was stirred at room temperature for 7 hours at a stirring speed of 600 r / min. The high-nickel ternary cathode material treated with the lithium monofluorophosphate solution was then placed in a vacuum drying oven at 100°C for 10 hours.

[0090] This step involves placing the high-nickel ternary cathode material in a lithium salt solution and stirring it at room temperature. This reaction involves lithium monofluorophosphate reacting with lithium carbonate and lithium hydroxide, allowing the residual alkali on the surface of the high-nickel ternary cathode material to fully react.

[0091] 3) The powder obtained after the reaction treatment in step 2) was added to ethanol and centrifuged at 9000 rpm for 3 minutes. After centrifugation twice, the powder was placed in an 80°C vacuum drying oven for 10 hours. The dried positive electrode powder was placed in a tube furnace under an oxygen atmosphere and sintered at a heating rate of 5°C / min to 650°C for 7 hours. After natural cooling, the repaired high-nickel ternary positive electrode material was obtained.

[0092] The addition of ethanol in this step dissolves residual lithium monofluorophosphate, thus preventing the resulting high-nickel ternary cathode material from being affected by residual lithium monofluorophosphate. Furthermore, a simple chemical reaction and sintering treatment facilitates structural repair of the material, transforming the rock salt structure into a layered structure.

[0093] 4) Assembling the high nickel ternary positive electrode material obtained in step 3) into a lithium battery.

[0094] Electrochemical testing of batteries assembled with the repaired cathode material revealed that the initial specific capacity of the repaired battery had returned to 180 mAh / g, an increase of nearly 20 mAh / g over the original capacity. Furthermore, the crystalline phase of the repaired material had returned to normal, demonstrating the effectiveness of the method.

[0095] Nickel-rich cathode materials are sensitive to trace amounts of moisture in the atmosphere and require extremely dry conditions for long-term storage. Once the surface of the nickel-rich cathode material is exposed to air, LiOH / Li2CO3 is formed. These impurities will hinder the insertion and extraction of Li and cause the loss of Li source. x F yThe solutions are mixed and stirred at room temperature to in-situ convert the LiOH / Li2CO3 failure layer into a Li3PO4 / LiF fast lithium-conducting interface. This conformal interface not only improves the air stability of the high-nickel ternary positive electrode material during storage, but also significantly enhances the interface lithium-conducting kinetics, improves the electrochemical rate performance, and at the same time isolates the electrolyte from corroding the positive electrode material, thereby improving the cycle stability. The process for removing residual alkali on the surface of the high-nickel ternary positive electrode material involved in the present invention is green and environmentally friendly, has a mild reaction, does not cause secondary pollution, and has simple equipment. It can be achieved only by stirring at room temperature and centrifuging. The process is simple, the cost is low, and industrial layout can be quickly realized.

[0096] The above-mentioned specific implementation methods are preferred examples of the present application. Although they are relatively detailed, they cannot limit the claims of the present application. Any changes, modifications, substitutions, combinations, and simplifications made using the technical content disclosed by the present invention should be equivalent embodiments, and should not deviate from the technical features of the present application. They should still fall within the scope of the technical features of the present application and should be included in the scope of protection of the present application.

[0097] Obviously, the above embodiments of the present application are merely examples for the purpose of clearly illustrating the present application, and are not intended to limit the embodiments of the present application. For those skilled in the art, other variations or modifications can be made based on the above description. It is not necessary and impossible to list all the embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present application shall be included within the scope of protection of the claims of the present application.

Claims

1. A method for removing residual alkali on the surface of high-nickel ternary positive electrode materials, characterized in that: The following steps are involved: (1) adding lithium salt to a green organic solvent, mixing, and stirring until clear without precipitation to prepare a lithium salt solution; (2) adding the air-depleted high-nickel ternary cathode material to the lithium salt solution, stirring and drying to obtain a powder; (3) The powder is centrifugally washed, dried, and sintered to obtain a repaired high-nickel ternary positive electrode material.

2. The method for removing residual alkali on the surface of high-nickel ternary cathode material according to claim 1, characterized in that: The lithium salt is one or more of lithium difluorophosphate, lithium hexafluorophosphate, lithium trifluorophosphate, and lithium monofluorophosphate.

3. The method for removing residual alkali on the surface of high-nickel ternary cathode material according to claim 1, characterized in that: In step (1), the green organic solvent is one or more of ethanol, methanol, ethylene glycol, propylene glycol, and isopropanol.

4. The method for removing residual alkali on the surface of high-nickel ternary cathode material according to claim 1, characterized in that: The mass fraction of lithium salt in the lithium salt solution is 1% to 5%.

5. The method for removing residual alkali on the surface of high-nickel ternary cathode material according to claim 1, characterized in that: The high-nickel ternary positive electrode material is a nickel-cobalt-manganese ternary positive electrode material or a nickel-cobalt-aluminum ternary positive electrode material.

6. The method for removing residual alkali on the surface of high-nickel ternary cathode material according to claim 1, characterized in that: In step (2), the mass ratio of the high-nickel ternary positive electrode material to the lithium salt solution is 1:10 to 50.

7. The method for removing residual alkali on the surface of high-nickel ternary cathode material according to claim 1, characterized in that: The stirring time in step (1) is 2 to 6 hours, and the stirring speed is 200-1000 r / min; the stirring time in step (2) is 5 to 48 hours, and the stirring speed is not less than 400 r / min.

8. The method for removing residual alkali on the surface of high-nickel ternary cathode material according to claim 1, characterized in that: In step (3), the washing is carried out using one or more of ethanol, methanol, ethylene glycol, propylene glycol, and isopropanol; the sintering temperature is 500-1000° C., and the sintering time is 5-12 hours.

9. A high nickel ternary cathode material, characterized in that: Prepared by the method according to any one of claims 1 to 8.

10. A lithium ion battery, characterized in that: The positive electrode material of the lithium-ion battery is prepared by the method according to any one of claims 1 to 8.

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