Lithium benzenetetracarboxylic acid-coated high-nickel positive electrode material as well as preparation method and application thereof

Abstract

The invention provides a lithium benzenetetracarboxylic acid-coated high-nickel positive electrode material as well as a preparation method and application thereof, and belongs to the technical field of preparation of positive electrode materials of lithium ion batteries. The high-nickel positive electrode material is obtained by mixing a high-nickel ternary precursor with lithium hydroxide and sintering the mixture in stages in a pure oxygen atmosphere; the preparation method comprises the following steps: adding the high-nickel positive electrode material into a mixed solution of pyromellitic acid and ethylene glycol, stirring for reaction, cooling, filtering, washing with absolute ethyl alcohol, and carrying out vacuum drying to successfully convert residual lithium on the surface into a lithium benzenetetracarboxylic acid coating layer in situ, thereby obtaining the lithium benzenetetracarboxylic acid coated high-nickel positive electrode material. According to the method, residual lithium of the high-nickel positive electrode material can be effectively removed, the formed lithium benzenetetracarboxylic acid coating layer has good ionic conductivity, side reaction of the material and electrolyte can be effectively isolated, and the interface stability is improved; meanwhile, transmission of lithium ions at an interface can be accelerated, polarization is reduced, and therefore the charging and discharging performance of the material is improved.

Description

[0001] This invention belongs to the field of lithium-ion battery cathode material preparation technology, specifically relating to a high-nickel cathode material coated with lithium phenyltetracarboxylate, its preparation method, and its application. Background Technology

[0002] High-nickel cathode materials have become key materials for next-generation lithium-ion batteries due to their high specific capacity and high energy density. However, residual lithium (mainly Li2CO3 and LiOH) on their surface is one of the key bottlenecks restricting their large-scale application, which can cause a series of problems: 1) Reaction with binders (such as PVDF) leads to slurry gelation, making coating difficult and affecting battery performance; 2) Reaction with electrolyte continuously generates CO2 / H2, causing battery swelling, increased internal pressure, and threatening safety; 3) Side reactions consume active lithium and generate high-resistivity interface films, leading to increased internal resistance, accelerated capacity decay, and shortened cycle life.

[0003] Currently, common methods for removing residual lithium from the surface of high-nickel cathode materials include surface coating synergistic treatment, direct washing (wet treatment), and thermal treatment (dry treatment). While surface coating synergistic treatment can remove residual lithium and form a coating layer, the process is cumbersome, requiring precise control of the coating agent concentration, reaction temperature, and time. Furthermore, uneven coating can lead to unremoved residual lithium in certain areas, causing localized electrolyte decomposition. For example, Chinese patent document CN118867200A discloses a nickel-rich ternary cathode material with a dual-modified structure, its preparation method, and its application. This method involves wet mixing of the high-nickel cathode material with a Ga source, evaporation to dryness, and then high-temperature sintering (720℃~780℃) to successfully convert residual lithium on the surface into a Li5GaO4 coating layer, thereby improving the charge-discharge performance of the high-nickel cathode material. However, this method is cumbersome and requires high-temperature sintering, resulting in high energy consumption and damage to the crystal structure due to the high-temperature treatment, as well as poor coating uniformity. Similar coating methods using Al, Zr, and Nb sources all face the same problems. Direct washing methods, such as water washing, alcohol washing, and acid washing, can directly remove residual lithium, which is low-cost and simple to operate, but cannot permanently eliminate the harmful effects of residual lithium. For example, while water washing can effectively remove residual lithium from the surface of high-nickel cathode materials, the Li₂ on the material surface... + It will react with H in the water + Ion exchange occurs, forming a NiOOH-like phase (such as Ni). 1~x H xAfter washing with water (using O2), the phase decomposes into lithium-deficient rock salt phase (NiO) or spinel phase (such as Ni3O4), disrupting the layered structure stability of the high-nickel cathode material. Furthermore, the material becomes more sensitive to air after washing, and after 30 days of storage, the residual lithium content on the surface increases to twice that of the unwashed material, thus accelerating performance degradation. Heat treatment avoids the dissolution and agglomeration problems of wet treatment, protecting the original structure of the material. The process is simple (only heating and cooling), making it suitable for integration with the cathode material sintering process. However, high-temperature heating (above 600℃) requires a large amount of energy, making the cost 3-5 times that of the wet method. Summary of the Invention

[0004] The purpose of this invention is to provide a high-nickel cathode material coated with lithium phenylenetetroxide, its preparation method, and its applications. This invention converts residual lithium on the surface of a high-nickel cathode material into a lithium phenylenetetroxide coating layer in situ. This method not only effectively removes residual lithium from the material surface, inhibits its reaction with CO2 and water in the air, and prevents gelation during electrode slurry preparation; simultaneously, the lower conversion temperature avoids damage to the material's crystal structure and is more energy-efficient. Furthermore, this preparation method achieves uniform coating of lithium phenylenetetroxide, and the resulting coating layer can mitigate side reactions between the material and the electrolyte during charging and discharging, reducing electrolyte consumption; at the same time, the good ionic conductivity of the lithium phenylenetetroxide coating layer can accelerate the ion transport rate during charging and discharging, thereby improving the material's charge-discharge performance.

[0005] To achieve the above objectives, the present invention provides the following technical solution: (1) A nickel-cobalt-manganese hydroxide precursor was mixed with lithium hydroxide and sintered in sections under a pure oxygen atmosphere to obtain a high-nickel cathode material. (2) The high-nickel cathode material was added to a mixed solution of pyromellitic acid and ethylene glycol, stirred and reacted, cooled, filtered, washed with anhydrous ethanol, and dried under vacuum to obtain a high-nickel cathode material coated with lithium pyromellitic acid.

[0006] Furthermore, in step (1), the chemical formula of the high-nickel ternary precursor is Ni 0.9 Co 0.05 Mn 0.05 (OH)2; the molar ratio of high-nickel ternary precursor to lithium hydroxide is 1:1.03~1.07; the segmented sintering conditions are: the first segment is sintered at 500~550℃ for 5~8h, and the second segment is sintered at 800~850℃ for 10~12h.

[0007] Further, in step (2), the molar ratio of pyromellitic acid to high-nickel cathode material is 0.5~1.0:100; the concentration of pyromellitic acid in the mixed solution of pyromellitic acid and ethylene glycol is 0.01~0.02mol / L; the stirring reaction temperature is 80~140℃ and the time is 24~36h; the number of times the anhydrous ethanol is washed is 3~5 times; the vacuum drying temperature is 80~100℃ and the time is 8~12h; the cooling condition is natural cooling to 20~30℃.

[0008] Another objective of this invention is to provide a method for preparing a high-nickel cathode material coated with lithium phenyltetracarboxylate obtained by the above-mentioned preparation method, wherein the cathode material has a surface coating of lithium phenyltetracarboxylate with a thickness of 20±5 nm.

[0009] Another objective of this invention is to provide the application of lithium phenyltetracarboxylate-coated high-nickel cathode materials, applying lithium phenyltetracarboxylate-coated high-nickel cathode materials to lithium battery cathodes.

[0010] Compared with the prior art, the present invention has the following advantages: 1) In this invention, during the synthesis of high-nickel cathode materials coated with lithium phenyltetracarboxylate, residual lithium on the surface of the high-nickel cathode material can be converted in situ into a lithium phenyltetracarboxylate coating layer by a low-temperature stirring reaction at 80℃~120℃. This low-temperature treatment process avoids damage to the crystal structure of the material and significantly reduces energy consumption. Simultaneously, this preparation method achieves uniform coating of phenyltetracarboxylate by reducing the "rate difference" between reaction and diffusion, minimizing the "capacity difference" between nucleation and growth, and reducing the "agglomeration tendency" of the coating agent during the coating process.

[0011] 2) In this invention, during the synthesis of high-nickel cathode materials coated with lithium phenylenetetroxide, the residual lithium on the surface of the high-nickel cathode material is converted in situ to lithium phenylenetroxide. This effectively solves the problem of electrode surface corrosion and performance degradation caused by the reaction of residual lithium on the surface of the high-nickel cathode with moisture and carbon dioxide in the air to form carbonates and other substances. Simultaneously, this conversion process significantly inhibits the acid-base reaction (saponification reaction) between residual alkali lithium on the surface of the high-nickel cathode material and the binder, thereby preventing gelation of the electrode slurry, ensuring good viscosity and fluidity of the slurry, guaranteeing uniform coating of the electrode slurry, and thus improving electrode quality.

[0012] 3) In this invention, the high-nickel cathode material coated with lithium phenylenetetracarboxylate is washed 3-5 times with anhydrous ethanol, which effectively removes the high-viscosity, easily residual ethylene glycol, preventing it from forming a non-conductive "insulating layer" during subsequent charging and discharging, thus hindering the transport of lithium ions between the cathode material and the electrolyte. The low residue of anhydrous ethanol also reduces its impact on slurry stability and improves the compatibility of the high-nickel cathode material with binders such as PVDF.

[0013] 4) In this invention, by controlling the stirring reaction temperature of 80℃~120℃ and the concentration of pyromellitic acid in the mixed solution of pyromellitic acid and ethylene glycol of 0.01~0.02mol / L during the synthesis of high-nickel cathode material coated with lithium pyromellitic acid, the complete coating of lithium pyromellitic acid is ensured, while avoiding the problems of local side reaction suppression failure and decrease in electronic conductivity caused by excessive coating thickness and uneven coating layer.

[0014] 5) In the present invention, during the synthesis of high-nickel cathode material coated with lithium phenyltetracarboxylate, the residual lithium on the surface of the high-nickel cathode material is converted in situ into a lithium phenyltetracarboxylate coating layer, which reduces the reaction between residual lithium and acidic substances in the electrolyte, effectively alleviates the consumption of effective components in the electrolyte, reduces the consumption rate of the electrolyte, and helps to extend the battery's service life.

[0015] 6) In this invention, during the synthesis of the high-nickel cathode material coated with lithium phenyltetracarboxylate, a uniform lithium phenyltetracarboxylate coating layer is formed on the surface of the high-nickel cathode material by controlling the stirring temperature and the concentration of the reaction solution. The thickness is within the range of 20±5 nm. This thickness range effectively avoids the failure of side reaction suppression caused by pinholes or cracks, and also prevents the coating layer from being too thick (>35 nm), which would lead to a decrease in the electronic conductivity of the high-nickel cathode material and its adverse effects on charge-discharge performance. Since lithium phenyltetracarboxylate has good ionic conductivity, this coating layer can effectively accelerate the transport of lithium ions between the electrode material and the electrolyte, thereby improving the charge-discharge efficiency and rate performance of the battery. Simultaneously, lithium phenyltetracarboxylate, as a beneficial component of the electrolyte additive, can optimize the electrode / electrolyte interface, reduce side reactions and electrolyte consumption, and improve the cycle stability of the battery.

[0016] 7) In the process of synthesizing lithium phenyltetracarboxylate-coated high-nickel cathode material, the removal of residual lithium on the surface of the high-nickel cathode material, the appropriate thickness of the lithium phenyltetracarboxylate coating layer, the protective effect of the lithium phenyltetracarboxylate coating layer, and the good ionic conductivity are achieved at a low conversion treatment temperature. When the lithium phenyltetracarboxylate-coated high-nickel cathode material is applied to the cathode of a lithium battery, it exhibits excellent performance. After 100 cycles at 1.0C, its capacity retention rate can reach 93.4% (2.7~4.5V). Attached Figure Description

[0017] Figure 1 This is a scanning electron microscope (SEM) image of the high-nickel cathode material coated with lithium phenylenetetracarboxylate in Example 1; Figure 2 This is a transmission electron microscope (TEM) image of the high-nickel cathode material coated with lithium phenylenetetracarboxylate in Example 1. Figure 3The image shows the X-ray diffraction (XRD) pattern of the high-nickel cathode material coated with lithium phenylenetetracarboxylate in Example 1. Figure 4 This is a comparison chart of the rate performance of the high-nickel cathode material coated with lithium phenylenetetracarboxylate in Example 1 and the high-nickel cathode material in Comparative Example 1; Figure 5 This is a comparison chart of the cycle performance of the high-nickel cathode material coated with lithium phenylenetetracarboxylate in Example 1 and the high-nickel cathode material in Comparative Example 1. Detailed Implementation

[0018] The present invention will be further described below with reference to embodiments and accompanying drawings, but the scope of protection of the present invention is not limited thereto.

[0019] The nickel-cobalt-manganese hydroxide precursor used in the embodiments and comparative examples of this invention is Ni. 0.9 Co 0.05 Mn 0.05 (OH)2; The method of this invention is also applicable to materials conforming to the chemical formula Ni x Co y Mn 1-x-y (OH)2 (0.9≤ x ≤0.95, 0≤y≤0.1, x High-nickel cathode materials are synthesized using other nickel-cobalt-manganese hydroxide precursors (+y=1).

[0020] Ni used in this invention 0.9 Co 0.05 Mn 0.05 The (OH)2 nickel cobalt manganese hydroxide precursor was purchased from Shenzhen Youyan Technology Co., Ltd. (product name: NCM9 series precursor); other medicines and reagents were purchased from Aladdin.com or Sinopharm Reagents.com. Example 1

[0021] (1) Ni precursor 0.9 Co 0.05 Mn 0.05 (OH)2 and LiOH are mixed evenly in a high-energy ball mill at a molar ratio of 1:1.05 to obtain a high-mixed material. The high-mixed material is then placed in a tube furnace and sintered in sections under a pure oxygen atmosphere. First, it is sintered at 550℃ for 5 hours, and then sintered at 800℃ for 12 hours. After sieving, a high-nickel cathode material is obtained. (2) Add 0.015 mol of pyromellitic acid to 1 L of ethylene glycol and stir at room temperature to dissolve, so as to obtain a mixed solution of pyromellitic acid and ethylene glycol with a concentration of 0.015 mol / L; take 1 mol of high nickel cathode material and add it to 500 mL of the mixed solution of pyromellitic acid and ethylene glycol, stir and react at 110 °C for 30 h, cool naturally to 20 °C, filter, wash 4 times with anhydrous ethanol, and dry under vacuum at 90 °C for 10 h to obtain lithium pyromellitic acid-coated high nickel cathode material.

[0022] Depend on Figure 2 As can be seen, the high-nickel cathode material coated with lithium phenylenetetracarboxylate has a coating layer with a thickness of approximately 20±5 nm. Example 2

[0023] (1) Ni precursor 0.9 Co 0.05 Mn 0.05 (OH)2 and LiOH are mixed evenly in a ball mill at a molar ratio of 1:1.03 to obtain a high-mixed material; the high-mixed material is then placed in a tube and sintered in sections under a pure oxygen atmosphere. First, it is sintered at 500°C for 8 hours, and then sintered at 800°C for 12 hours. After sieving, a high-nickel cathode material is obtained. (2) 0.010 mol of pyromellitic acid was added to 1 L of ethylene glycol and stirred at room temperature to dissolve, resulting in a mixed solution of pyromellitic acid and ethylene glycol with a concentration of 0.010 mol / L. 1 mol of high-nickel cathode material was added to 500 mL of the mixed solution of pyromellitic acid and ethylene glycol and stirred at 140 °C for 24 h. The mixture was then cooled to 30 °C, filtered, washed 5 times with anhydrous ethanol, and dried under vacuum at 80 °C for 12 h to obtain lithium pyromellitic acid-coated high-nickel cathode material. Example 3

[0024] (1) Ni precursor 0.9 Co 0.05 Mn 0.05 (OH)2 and LiOH are mixed evenly in a ball mill at a molar ratio of 1:1.07 to obtain a high-mixed material; the high-mixed material is then placed in a tube furnace and sintered in sections under a pure oxygen atmosphere. First, it is sintered at 550°C for 5 hours, and then sintered at 850°C for 10 hours. After sieving, a high-nickel cathode material is obtained. (2) Add 0.020 mol of pyromellitic acid to 1 L of ethylene glycol and stir at room temperature to dissolve, so as to obtain a mixed solution of pyromellitic acid and ethylene glycol with a concentration of 0.020 mol / L; take 1 mol of high nickel cathode material and add it to 500 mL of the mixed solution of pyromellitic acid and ethylene glycol, stir and react at 80 °C for 36 h, cool to 25 °C, filter, wash 3 times with anhydrous ethanol, and dry under vacuum at 100 °C for 8 h to obtain lithium pyromellitic acid-coated high nickel cathode material. Example 4

[0025] (1) Ni precursor 0.9 Co 0.05 Mn 0.05 (OH)2 and LiOH are mixed evenly in a ball mill at a molar ratio of 1:1.05 to obtain a high-mixed material; the high-mixed material is then placed in a tube furnace and sintered in sections under a pure oxygen atmosphere. First, it is sintered at 520°C for 7 hours, and then sintered at 830°C for 11 hours. After sieving, a high-nickel cathode material is obtained. (2) Add 0.015 mol of pyromellitic acid to 1 L of ethylene glycol and stir at room temperature to dissolve, so as to obtain a mixed solution of pyromellitic acid and ethylene glycol with a concentration of 0.015 mol / L; take 1 mol of high nickel cathode material and add it to 500 mL of the mixed solution of pyromellitic acid and ethylene glycol, stir and react at 110 °C for 30 h, cool to 25 °C, filter, wash 4 times with anhydrous ethanol, and dry under vacuum at 90 °C for 10 h to obtain lithium pyromellitic acid-coated high nickel cathode material. Comparative Example 1

[0026] Similar to the steps in Example 1, except that pyromellitic acid was not added in step (2).

[0027] (1) Ni precursor 0.9 Co 0.05 Mn 0.05 (OH)2 and LiOH are mixed evenly in a ball mill at a molar ratio of 1:1.05 to obtain a high-mixed material; the high-mixed material is then placed in a tube furnace and sintered in sections under a pure oxygen atmosphere. First, it is sintered at 550°C for 5 hours, and then sintered at 800°C for 12 hours. After sieving, a high-nickel cathode material is obtained. (2) Take 1 mol of high-nickel cathode material and add it to 500 ml of ethylene glycol. Stir and react at 110 °C for 30 h. Cool to 25 °C, filter, wash 4 times with anhydrous ethanol, and dry under vacuum at 90 °C for 10 h to obtain uncoated high-nickel cathode material. Comparative Example 2

[0028] Similar to the steps in Example 1, the only difference is that in step (2), the stirring is carried out at room temperature.

[0029] (1) Ni precursor 0.9 Co 0.05 Mn 0.05 (OH)2 and LiOH are mixed evenly in a ball mill at a molar ratio of 1:1.05 to obtain a high-mixed material; the high-mixed material is then placed in a tube furnace and sintered in sections under a pure oxygen atmosphere. First, it is sintered at 550°C for 5 hours, and then sintered at 800°C for 12 hours. After sieving, a high-nickel cathode material is obtained. (2) Add 0.015 mol of pyromellitic acid to 1 L of ethylene glycol and stir at room temperature to dissolve, so as to obtain a mixed solution of pyromellitic acid and ethylene glycol with a concentration of 0.015 mol / L; take 1 mol of high nickel cathode material and add it to 500 mL of the mixed solution of pyromellitic acid and ethylene glycol, stir at room temperature for 30 h, cool to 25 °C, filter, and dry with anhydrous ethanol under vacuum at 90 °C for 10 h to obtain room temperature high nickel cathode material. Comparative Example 3

[0030] Similar to the steps in Example 1, except that anhydrous ethanol is not used for washing in step (2).

[0031] (1) Ni precursor 0.9 Co 0.05 Mn 0.05 (OH)2 and LiOH are mixed evenly in a ball mill at a molar ratio of 1:1.05 to obtain a high-mixed material; the high-mixed material is then placed in a tube furnace and sintered in sections under a pure oxygen atmosphere. First, it is sintered at 550°C for 5 hours, and then sintered at 800°C for 12 hours. After sieving, a high-nickel cathode material is obtained. (2) Add 0.015 mol of pyromellitic acid to 1 L of ethylene glycol and stir at room temperature to dissolve, so as to obtain a mixed solution of pyromellitic acid and ethylene glycol with a concentration of 0.015 mol / L; take 1 mol of high nickel cathode material and add it to 500 mL of the mixed solution of pyromellitic acid and ethylene glycol, stir and react at 110 °C for 30 h, cool to room temperature, filter, and dry under vacuum at 90 °C for 10 h to obtain high nickel cathode material coated with unwashed lithium pyromellitic acid. Comparative Example 4

[0032] Similar to the steps in Example 1, except that the stirring temperature in step (2) is increased.

[0033] (1) Ni precursor 0.9 Co 0.05 Mn 0.05(OH)2 and LiOH are mixed evenly in a high-energy ball mill at a molar ratio of 1:1.05 to obtain a high-mixed material; the high-mixed material is then placed in a tube furnace and sintered in sections under a pure oxygen atmosphere. First, it is sintered at 550°C for 5 hours, and then sintered at 800°C for 12 hours. After sieving, a high-nickel cathode material is obtained. (2) Add 0.015 mol of pyromellitic acid to 1 L of ethylene glycol and stir at room temperature to dissolve, so as to obtain a mixed solution of pyromellitic acid and ethylene glycol with a concentration of 0.015 mol / L; take 1 mol of high nickel cathode material and add it to 500 mL of the mixed solution of pyromellitic acid and ethylene glycol, stir and react at 160 °C for 30 h, filter and wash 4 times, and dry under vacuum at 90 °C for 10 h to obtain high nickel cathode material coated with lithium pyromellitic acid. Comparative Example 5

[0034] Similar to the steps in Example 1, except that the concentration of pyromellitic acid in the mixed solution in step (2) is reduced.

[0035] (1) Ni precursor 0.9 Co 0.05 Mn 0.05 (OH)2 and LiOH are mixed evenly in a high-energy ball mill at a molar ratio of 1:1.05 to obtain a high-mixed material. The high-mixed material is then placed in a tube furnace and sintered in sections under a pure oxygen atmosphere. First, it is sintered at 550℃ for 5 hours, and then sintered at 800℃ for 12 hours. After sieving, a high-nickel cathode material is obtained. (2) Add 0.005 mol of pyromellitic acid to 1 L of ethylene glycol and stir at room temperature to dissolve, so as to obtain a mixed solution of pyromellitic acid and ethylene glycol with a concentration of 0.005 mol / L; take 1 mol of high nickel cathode material and add it to 500 mL of the mixed solution of pyromellitic acid and ethylene glycol, stir and react at 110 °C for 30 h, cool naturally to 20 °C, filter, wash 4 times with anhydrous ethanol, and dry under vacuum at 90 °C for 10 h to obtain lithium pyromellitic acid-coated high nickel cathode material. Comparative Example 6

[0036] Similar to the steps in Example 1, except that the concentration of pyromellitic acid in the mixed solution in step (2) is increased.

[0037] (1) Ni precursor 0.9 Co 0.05 Mn 0.05 (OH)2 and LiOH are mixed evenly in a high-energy ball mill at a molar ratio of 1:1.05 to obtain a high-mixed material. The high-mixed material is then placed in a tube furnace and sintered in sections under a pure oxygen atmosphere. First, it is sintered at 550℃ for 5 hours, and then sintered at 800℃ for 12 hours. After sieving, a high-nickel cathode material is obtained. (2) Add 0.030 mol of pyromellitic acid to 1 L of ethylene glycol and stir at room temperature to dissolve, so as to obtain a mixed solution of pyromellitic acid and ethylene glycol with a concentration of 0.030 mol / L; take 1 mol of high nickel cathode material and add it to 500 mL of the mixed solution of pyromellitic acid and ethylene glycol, stir and react at 110 °C for 30 h, cool naturally to 20 °C, filter, wash 4 times with anhydrous ethanol, and dry under vacuum at 90 °C for 10 h to obtain lithium pyromellitic acid-coated high nickel cathode material. Experimental results

[0038] Depend on Figure 1 and Figure 2 As can be seen, the lithium phenylenetetroxide-coated high-nickel cathode material obtained in Example 1 shows obvious coating on its surface, with a coating thickness of approximately 20 nm ± 5 nm. Meanwhile, from Figure 3 The XRD pattern of the high-nickel cathode material coated with lithium phenylene terephthalate shows that the characteristic peak intensity of the high-nickel cathode material is high and there are no other impurity peaks. This indicates that the in-situ conversion treatment will not damage the structure of the material itself.

[0039] The lithium phenylene tetracarboxylate-coated high-nickel cathode material provided by this invention is used as the cathode material for lithium-ion batteries to assemble batteries, and electrochemical performance tests are conducted: The high-nickel cathode material coated with lithium phenylene tetracarboxylate, acetylene black (conductive agent), and polyvinylidene fluoride (binder) are ground thoroughly and uniformly in an agate mortar at a mass ratio of 9:0.5:0.5. N-methylpyrrolidone (NMP) is added to form a uniform slurry, which is then coated onto an aluminum foil current collector as a test electrode. A coin cell is assembled using lithium metal as the counter electrode. The electrolyte used is 1.0M LiPF6 in DMC:EC:EMC=1:1:1 Vol% / L. The battery is charged and discharged 5 times at a 0.1C rate, and then cycled 100 times at a 1.0C rate. The voltage range is 2.7~4.5V. The test results are shown in Table 1.

[0040] As shown in Table 1, the batteries assembled with the lithium phenylenetetroxide-coated high-nickel cathode materials obtained in Examples 1-4 have higher initial discharge capacity and better cycle performance than the lithium batteries assembled with the cathode materials prepared in Comparative Examples 1-6. Furthermore, from... Figure 4 and Figure 5As can be seen, the lithium phenylene oxide-coated high-nickel cathode material obtained by in-situ conversion of residual lithium on the surface of the high-nickel cathode material exhibits better charge-discharge performance, with an initial capacity of 216 mAh / g and a capacity retention rate of 93.4% after 100 cycles at 1.0C. This is mainly due to the addition of pyromellitic acid, which, under suitable conditions, converts the residual lithium on the surface of the high-nickel cathode material into a lithium phenylene oxide coating layer in situ. This not only effectively consumes the residual lithium on the surface of the high-nickel cathode material, reducing gelation of the electrode slurry, improving the slurry's fluidity and viscosity, and ensuring the coating quality of the electrode, but also enhances the material's air stability through the lithium phenylene oxide coating layer. Furthermore, the lithium phenylene oxide coating layer reduces the occurrence of side reactions between the material and the electrolyte, and the coating layer's excellent ion conductivity accelerates lithium-ion interfacial transport, thereby effectively improving the material's discharge capacity and cycle stability. Conversely, the uncoated high-nickel material obtained in Comparative Example 1 without the addition of pyromellitic acid exhibited lower initial discharge capacity (200 mAh / g) and cycle retention (76.7%), due to the lack of lithium pyromellitic acid coating. The room-temperature high-nickel cathode material obtained in Comparative Example 2 showed poor initial capacity and cycle performance, primarily because the added pyromellitic acid could not react with residual lithium on the material surface during room-temperature stirring, failing to form a lithium pyromellitic acid coating layer. The poor initial capacity and cycle performance of the high-nickel cathode material obtained in Comparative Example 3 was due to the absence of washing with anhydrous ethanol, resulting in high-viscosity, easily residual ethylene glycol that generated a non-conductive "insulating layer" during charging and discharging, hindering lithium-ion transport between the cathode material and the electrolyte, leading to poor material performance. The poor initial capacity and cycle performance of the lithium pyromellitic acid-coated high-nickel cathode material obtained in Comparative Example 4 were due to two factors: firstly, the excessively high stirring temperature resulted in an overly thick coating layer, reducing the electronic conductivity of the high-nickel cathode material; secondly, the excessively high temperature led to uneven coating. The lithium pyromellitic acid-coated high-nickel cathode material obtained in Comparative Example 5 had incomplete lithium pyromellitic acid coating due to insufficient coating amount, resulting in poor coating effect and consequently poor charge-discharge performance. The poor charge-discharge performance of the lithium pyromellitic acid-coated high-nickel cathode material obtained in Comparative Example 6 was mainly due to the excessively high concentration of pyromellitic acid in the mixed solution, leading to excessive coating and reduced electronic conductivity of the material.

[0041] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a high-nickel cathode material coated with lithium phenylenetetracarboxylate, characterized in that, The steps are as follows: (1) A nickel-cobalt-manganese hydroxide precursor was mixed with lithium hydroxide and sintered in sections under a pure oxygen atmosphere to obtain a high-nickel cathode material. (2) The high-nickel cathode material was added to a mixed solution of pyromellitic acid and ethylene glycol, stirred and reacted, cooled, filtered, washed with anhydrous ethanol, and vacuum dried to obtain lithium pyromellitic acid-coated high-nickel cathode material. In step (1), the molar ratio of nickel cobalt manganese hydroxide precursor to lithium hydroxide is 1:1.03~1.07; The sintering conditions are as follows: the first stage is sintered at 500~550℃ for 5~8h, and the second stage is sintered at 800~850℃ for 10~12h; in step (2), the stirring reaction temperature is 80~140℃ and the time is 24~36h; the cooling condition is natural cooling to 20~30℃.

2. The method for preparing the lithium phenylenetetracarboxylate-coated high-nickel cathode material according to claim 1, characterized in that, In step (2), the molar ratio of pyromellitic acid to high-nickel cathode material is 0.5~1.0:100; the concentration of pyromellitic acid in the mixed solution of pyromellitic acid and ethylene glycol is 0.01~0.02 mol / L.

3. The method for preparing the lithium phenylenetetracarboxylate-coated high-nickel cathode material according to claim 1, characterized in that, In step (2), the anhydrous ethanol washing is performed 3 to 5 times; the vacuum drying temperature is 80 to 100°C and the time is 8 to 12 hours.

4. A high-nickel cathode material coated with lithium phenylenetetracarboxylate prepared by the preparation method according to any one of claims 1-3, characterized in that, The surface coating of the high-nickel cathode material is lithium phenyltetracarbonate with a thickness of 20±5nm.

5. The application of a high-nickel cathode material coated with lithium phenylenetetracarboxylate as described in claim 4, characterized in that, High-nickel cathode materials coated with lithium phenyltetracarboxylate are applied to the cathode of lithium batteries.

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