In-situ coated nickel-rich ternary positive electrode material, and preparation method and application thereof

Abstract

The application relates to the technical field of positive electrode materials, in particular to a nickel-rich ternary positive electrode material coated in situ, a preparation method and application thereof. The preparation method is as follows: perfluoro (2-methyl-3-oxa hexanoic acid) or perfluorooctanoic acid is dissolved in an organic solvent to configure solution A; the nickel-rich ternary positive electrode material dried in vacuum is immersed in the solution A, and heating and stirring are carried out until the organic solvent is dried, so that the nickel-rich ternary positive electrode material coated in situ is obtained. The perfluorinated compound reacts in situ with the residual surface of the nickel-rich ternary positive electrode material and lithium hydroxide to generate lithium perfluorooctanoate, which is converted into LiF and Li2O in the subsequent electrochemical defluorination process, the electrolyte corrosion to the positive electrode can be inhibited, the lithium ion can be promoted to migrate along the heterojunction formed by LiF and Li2O quickly, the rate performance and long cycle stability of the lithium ion battery are improved, and the degradation and removal of the perfluorinated compound are realized.

Description

Technical Field

[0001] This invention relates to the field of cathode material technology, and in particular to an in-situ coated nickel-rich ternary cathode material, its preparation method, and its application. Background Technology

[0002] Ternary cathode materials, due to their superior performance in capacity and cycle life, have a significant advantage in the high-energy-density application market and have become the mainstream choice for new energy power batteries. Increasing the upper limit cutoff voltage of ternary cathode materials can result in even higher capacity and energy density. However, increasing the cutoff voltage leads to extensive chemical-physical failure processes, resulting in irreversible phase transitions. Simultaneously, it exposes the internal structure to the electrolyte, causing side reactions, structural failure, capacity reduction, and even safety issues.

[0003] Therefore, improving the cutoff voltage of nickel-rich ternary cathode materials while overcoming the side reactions between their internal structure and electrolyte caused by phase transition is key to promoting the large-scale industrial application of nickel-rich ternary cathode materials, and is of great significance to the development and application of lithium-ion battery technology. Summary of the Invention

[0004] The purpose of this invention is to address the aforementioned shortcomings of the prior art by proposing an in-situ coated nickel-rich ternary cathode material, its preparation method, and its application.

[0005] The first objective of this invention is to provide a method for preparing an in-situ coated nickel-rich ternary cathode material, comprising the following steps: Solution A is prepared by dissolving perfluoro(2-methyl-3-oxahexanoic acid) or perfluorooctanoic acid in an organic solvent; The vacuum-dried nickel-rich ternary cathode material is immersed in solution A and heated and stirred until the organic solvent evaporates to obtain in-situ coated nickel-rich ternary cathode material.

[0006] 10. Further, the concentration of solution A is 1.5 g / L, and the mass-to-volume ratio of nickel-rich ternary cathode material to solution A is 1 g: 50 mL-200 mL.

[0007] Furthermore, the organic solvent is one of methanol, ethanol, and tetrahydrofuran.

[0008] Furthermore, the heating and stirring temperature is 80-120 ℃.

[0009] A second objective of this invention is to provide an in-situ coated nickel-rich ternary cathode material prepared by the preparation method described above.

[0010] A third objective of this invention is to provide a positive electrode sheet for a lithium-ion battery, comprising the aforementioned in-situ coated nickel-rich ternary positive electrode material.

[0011] The fourth objective of this invention is to provide a method for preparing a positive electrode sheet for a lithium-ion battery as described above, characterized in that the in-situ coated nickel-rich ternary positive electrode material is mixed with a binder and a conductive agent, NMP is added and stirred to form a slurry, and the slurry is coated on an aluminum foil to obtain a positive electrode sheet.

[0012] Furthermore, the binder is PVDF, the conductive agent is Super P Li, and the mass ratio of the in-situ coated nickel-rich ternary cathode material to the binder and conductive agent is 90:5:5.

[0013] A fifth objective of the present invention is to provide a lithium-ion battery, including the positive electrode of a lithium-ion battery as described above.

[0014] This invention uses recalcitrant perfluorinated compounds (2-methyl-3-oxahexanoic acid) or perfluorooctanoic acid as raw materials. A perfluorinated compound solution is prepared by dissolving these compounds in solvents (methanol, ethanol, tetrahydrofuran, etc.). Subsequently, a vacuum-dried nickel-rich ternary cathode material is placed in the perfluorinated compound solution and stirred and evaporated at a low temperature. This allows the perfluorinated compound to react in situ with residual lithium hydroxide (LiOH) on the surface of the nickel-rich ternary cathode material, producing lithium perfluorooctanoate (PFOALi). In the subsequent electrochemical defluorination process, it is converted into LiF and Li₂O. LiF, as a stable cathode electrolyte interface (CEI) layer component, can inhibit electrolyte corrosion of the cathode. Li₂O, as a fast ion transport medium, can promote the rapid migration of lithium ions along the heterogeneous grain boundaries formed by LiF and Li₂O, thereby significantly improving the material's kinetic performance. In subsequent lithium-ion battery tests, it exhibited excellent rate performance and long cycle stability, while simultaneously achieving the degradation and removal of perfluorinated compounds. This method is simple, environmentally friendly, low-cost, and can be mass-produced, providing a reference for the surface modification of other cathode materials.

[0015] Compared with the prior art, the advantages of the present invention are as follows: 1. Innovatively utilizing the unavoidable LiOH on the surface of nickel-rich ternary cathode materials, a new experimental scheme is provided for the modification of cathode materials for lithium-ion batteries; 2. Innovatively utilize PFOA, a pollutant that is difficult to process naturally, to improve the performance of lithium-ion cathode materials while treating hazardous waste; 3. This invention utilizes the low-temperature reaction of PFOA, which is difficult to degrade in nature, with residual LiOH on the surface of nickel-rich ternary cathode materials. The raw materials are simple, the cost is low, the process is environmentally friendly, the process is simple and easy to implement, and it can be produced on a large scale. 4. The modified cathode material exhibits excellent electrochemical performance. Attached Figure Description

[0016] Figure 1 This is the first charge-discharge curve of the positive electrode sheet prepared in Example 2; Figure 2 This is a 1C cycle performance diagram of the positive electrode sheet prepared in Example 2; Figure 3 This is a 3C cycle performance diagram of the positive electrode sheet prepared in Example 2; Figure 4 This is a rate performance diagram of the positive electrode sheet prepared in Example 2; Figure 5 These are scanning electron microscope (SEM) images and EDS images of the in-situ coated nickel-rich ternary cathode material prepared in Example 2; Figure 6 This is the XPS image of the in-situ coated nickel-rich ternary cathode material prepared in Example 2; Figure 7 This is a 1C cycle performance diagram of the positive electrode sheet prepared in Comparative Example 1; Figure 8 This is a graph showing the 1C cycle performance of the nickel-rich ternary cathode material in Comparative Example 2 in an electrolyte containing PFOA. Detailed Implementation

[0017] The following are specific embodiments of the present invention, which are described in conjunction with the accompanying drawings. However, the present invention is not limited to these embodiments.

[0018] The nickel-rich ternary cathode materials purchased in the examples and comparative examples were all purchased from Beijing Easpring Material Technology Co., Ltd. (CZ-ME83SC-23030101).

[0019] Example 1 Step 1: Vacuum dry the purchased nickel-rich ternary cathode material in a 120 ℃ oven; Step 2: Prepare a 1.5 g / L solution A using 0.15 g of perfluorooctanoic acid (PFOA) as the solute and methanol as the solvent; Step 3: Immerse 1 g of dried nickel-rich ternary cathode material in 100 ml of solution A and heat and stir until the solvent evaporates to dryness to obtain the product; Step 4: Mix the nickel-rich ternary cathode material obtained in Step 3 with binder (PVDF) and conductive agent (Super PLi) in a ratio of 90:5:5, add NMP, stir for 2 hours, and then coat to obtain the cathode sheet.

[0020] Example 2 The methanol in Example 1 was replaced with ethanol, and everything else was the same as in Example 1.

[0021] The positive electrode prepared in Example 2 was vacuum dried and then assembled into a coin cell for electrochemical performance testing.

[0022] Figure 1 The first charge-discharge curve of the positive electrode prepared in Example 2 at a current density of 0.1 C is shown. The material has a good first coulombic efficiency of 87.5%, which is attributed to the protective effect of the in-situ coated PFOALi during the first charge-discharge process at high voltage. Figure 2 The positive electrode prepared in Example 2 is shown in the cycling diagram at a current density of 1 C and a voltage of 2.7-4.5 V. After 100 cycles, it maintains a strength of 157.4 mAh g. -1 The discharge specific capacity, with a capacity retention rate of 86.5%, is attributed to the defluorination of the surface coating PFOALi during electrochemical cycling, which transforms it into LiF, generating a stable CEI layer rich in LiF. This prevents the electrolyte from corroding the internal structure and greatly improves the cycle stability of the cathode material.

[0023] Figure 3 The positive electrode prepared in Example 2 is shown in the cycling diagram at a current density of 3 C and a voltage of 2.7-4.5 V. After 200 cycles, it retains 137.2 mAh g⁻¹. -1 The discharge specific capacity and capacity retention rate are 81.7%, which is attributed to the transformation of the surface coating layer PFOALi into LiF during cycling. At the same time, the stable CEI layer on the surface protects the internal structure and prevents the internal structure of the ternary cathode material from being corroded by the electrolyte during high current and high voltage cycling due to phase transition.

[0024] Figure 4 The rate performance of the positive electrode prepared in Example 2 remained at approximately 171 mAh g⁻¹ at a current density of 5 C. -1 The high specific capacity is attributed to the conversion of PFOALi into LiF and Li2O during cycling. Li2O, as a fast ion transport medium, can promote the rapid migration of lithium ions along the heterogeneous grain boundaries formed by LiF and Li2O, thereby significantly improving the kinetic performance of the material.

[0025] Figure 5 The images shown are scanning electron microscope (SEM) and EDS images of the in-situ coated nickel-rich ternary cathode material prepared in Example 2. It was observed that PFOA reacts in situ with LiOH on the surface of the nickel-rich ternary cathode material, resulting in a uniform and dense coating.

[0026] Figure 6 XPS images of the in-situ coated nickel-rich ternary cathode material demonstrate the successful coating of POFALi on the surface.

[0027] Comparative Example 1 Step 1: Vacuum dry the purchased nickel-rich ternary cathode material in a 120 ℃ oven; Step 2: Mix the nickel-rich ternary cathode material with binder (PVDF) and conductive agent (Super P Li) in a ratio of 90:5:5, add NMP, stir for 2 hours, and then coat to obtain the cathode sheet.

[0028] Figure 7 The graph shows the 1C cycle performance of the positive electrode prepared in Comparative Example 1. At a current density of 1C and a voltage of 2.7-4.5 V, the uncoated nickel-rich ternary positive electrode material retains only 111 mAh g⁻¹ after 100 cycles. -1 The capacity retention rate was 64.9%.

[0029] Comparative Example 2 Step 1: Vacuum dry the purchased nickel-rich ternary cathode material in a 120 ℃ oven; Step 2: Mix the nickel-rich ternary cathode material with binder (PVDF) and conductive agent (Super P Li) in a ratio of 90:5:5, add NMP, stir for 2 hours, and then coat to obtain the cathode sheet; Step 3: Add PFOALi to LB-046 electrolyte and stir until homogeneous to obtain an electrolyte containing PFOALi additive, and then encapsulate and test the battery.

[0030] Figure 8 The graph shows the cycling performance of the uncoated nickel-rich ternary cathode material in a PFOALi electrolyte. At a current density of 1 C and a voltage range of 2.7–4.5 V, the ternary cathode material retains only 128.7 mAh g⁻¹ after 100 cycles. -1 The capacity retention rate was 75%, which was due to the addition of PFOALi to the electrolyte without residual alkali treatment, which led to the generation of HF during cycling and damaged the structure.

[0031] For any points not covered above, existing technologies shall apply.

[0032] Although specific embodiments of the present invention have been described in detail by way of examples, those skilled in the art should understand that the above examples are for illustrative purposes only and are not intended to limit the scope of the invention. Those skilled in the art can make various modifications or additions to the described specific embodiments or use similar methods to replace them, without departing from the direction of the invention or exceeding the scope defined by the appended claims. Those skilled in the art should understand that any modifications, equivalent substitutions, improvements, etc., made to the above embodiments based on the technical essence of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing an in-situ coated nickel-rich ternary cathode material, characterized in that, Includes the following steps: Solution A is prepared by dissolving perfluoro(2-methyl-3-oxahexanoic acid) or perfluorooctanoic acid in an organic solvent; The vacuum-dried nickel-rich ternary cathode material is immersed in solution A and heated and stirred until the organic solvent evaporates to obtain the in-situ coated nickel-rich ternary cathode material.

2. The preparation method according to claim 1, characterized in that, The concentration of solution A is 1.5 g / L, and the mass-to-volume ratio of nickel-rich ternary cathode material to solution A is 1 g: 50 mL - 200 mL.

3. The preparation method according to claim 1, characterized in that, The organic solvent is one of methanol, ethanol, and tetrahydrofuran.

4. The preparation method according to claim 1, characterized in that, The heating and stirring temperature is 80-120 ℃.

5. An in-situ coated nickel-rich ternary cathode material prepared by the preparation method according to any one of claims 1-4.

6. A positive electrode sheet for a lithium-ion battery, characterized in that, Including the in-situ coated nickel-rich ternary cathode material as described in claim 5.

7. A method for preparing the positive electrode sheet of a lithium-ion battery as described in claim 6, characterized in that, The in-situ coated nickel-rich ternary cathode material is mixed with a binder and a conductive agent, NMP is added and stirred to form a slurry, and the slurry is coated on aluminum foil to obtain a cathode sheet.

8. The preparation method according to claim 7, characterized in that, The binder is PVDF, the conductive agent is Super PLi, and the mass ratio of the in-situ coated nickel-rich ternary cathode material to the binder and conductive agent is 90:5:

5.

9. A lithium-ion battery, characterized in that, Includes the positive electrode of the lithium-ion battery as described in claim 6.

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