Method for reducing residual alkali on surface of high-nickel ternary electrode material

Abstract

The application discloses a method for reducing residual alkali on the surface of high-nickel ternary electrode material, which comprises the following steps: mixing the high-nickel ternary electrode material with a washing solution containing deionized water and an organic long-chain fatty acid solution, stirring and washing, and then performing solid-liquid separation to obtain a solid product. The method utilizes the synergistic coupling effect of the deionized water and the organic long-chain fatty acid solution, can effectively remove the residual alkali impedance layer on the surface of the high-nickel ternary material, greatly improves the removal efficiency of the residual alkali on the surface of the high-nickel ternary electrode material, and significantly enhances the structural thermal stability, capacity rate performance and safety performance of the high-nickel ternary electrode material. In addition, the method is simple, low in cost, energy-saving and environment-friendly, and can be widely applied to subsequent processing and modification treatment of commercial high-nickel NCM ternary layered positive electrode material.

Description

Technical Field

[0001] This invention relates to a surface treatment method for high-nickel ternary electrode materials, and particularly to a method for reducing residual alkali on the surface of high-nickel ternary electrode materials, belonging to the field of battery material technology. Background Technology

[0002] The rapid depletion of non-renewable energy sources (coal, oil, etc.) has led to severe environmental pollution, prompting widespread attention to clean energy in recent years. However, the intermittent and unsustainable nature of clean energy makes stable energy supply difficult, thus necessitating the development of efficient energy storage devices. Lithium-ion batteries, with their high energy density, environmental friendliness, long cycle life, low self-discharge rate, and lack of memory effect, have stood out among various energy storage devices (liquid batteries, flywheel energy storage, etc.), becoming the preferred power source for portable mobile devices and electric vehicles. With the rapid development of new energy electric vehicles, the demand for high-energy-density power batteries is increasing, making the improvement of lithium-ion battery energy density a current focus. As a key component of lithium-ion battery energy storage systems, the development of high-energy-density cathode materials has attracted widespread attention from researchers, potentially meeting the urgent needs of the commercial and mobile terminal markets for high-energy-density energy storage systems. 1-x-y Co x Mn y O2(NCM) ternary layered cathode material combines the advantages of LiCoO2, LiNiO2 and LiMnO2 materials, and has the advantages of high discharge specific capacity, high energy density, low toxicity and low cost, making it a highly promising candidate for lithium-ion battery cathode material.

[0003] Nickel-cobalt-manganese ternary layered cathode material LiN x Co y Mn zO2(x+y+z=1), abbreviated as NCM, is a ternary electrode material with an α-NaFeO2 type layered structure, belonging to the hexagonal crystal system, R-3m space group. Li and the three transition metal elements Ni, Co, and Mn alternately occupy the 3a and 3b positions, while oxygen ions occupy the 6c position, existing in a cubic packing form. Based on the content ratio of the transition metal element Ni in the NCM ternary system, it is divided into low-nickel ternary (x<0.6) and high-nickel ternary (x≥0.6) cathode materials. Examples include NCM523, NCM424, and NCM111, which are low-nickel ternary cathode materials, while NCM811, NCM721, and NCM622 are high-nickel ternary cathode materials. High-nickel NCM ternary layered cathode materials, due to their high nickel content, significantly improve the specific capacity and energy density of the material, while greatly reducing the material cost. However, high-nickel materials with a nickel content of over 80% will experience surface side reactions that induce a sharp increase in the LiOH / Li2CO3 (RLCs) ratio. Currently, the formation mechanism of RLCs on the surface of high-nickel materials can be attributed to the following three points: (1) During the preparation process, the high-nickel NCM ternary layered cathode material needs to add an excess of lithium source to balance the evaporation of lithium during the high-temperature treatment and suppress the Li + / Ni 2+ Mixed arrangement, and supporting the hexagonal layered structure of high-nickel ternary cathode material, resulting in some lithium source deposited on the surface of the material to form lithium residue; (2) During storage, residual lithium is sensitive to air, easily absorbs moisture, and easily reacts with H2O and CO2 in the air to generate RLCs; (3) Ni in high-nickel ternary material 3+ It is unstable and readily reduced to Ni during storage and electrochemical cycling. 2+ , lattice oxygen O 2- It will be oxidized to O - Ultimately, reactive oxygen species (O2) are formed on the material surface. 2- reactive oxygen species (O2) 2- Same as Li + Lithium oxides (LiO) are formed and react with H2O and CO2 in the air to form lithium chromatographs (RLCs). The presence of RLCs poses a serious challenge to the preparation, storage and application of high-nickel NCM ternary layered cathode materials: (1) Microcracks: Due to the high nickel content (≥60%), high-nickel NCM ternary layered cathode materials generate more RLCs through surface side reactions, which exacerbates the change in lattice parameters along the c-axis and makes microcrack propagation more severe; (2) Li + / Ni 2+ Mixed arrangement, Ni 2+ radius is The radius of Li+ is Due to the sensitivity of high-nickel materials to H2O and CO2 in the air, surface RLCs increase sharply, accompanied by Ni 3+ / Ni 2+ The reduction of Ni 2+Will spontaneously occupy Li + The large number of empty spaces left by the embedding exacerbates Li's + / Ni 2+ The degree of mixing; in addition, the more serious Li caused by residual alkali. + / Ni 2+ The disordered arrangement can reduce the distance between lithium layers, significantly hindering lithium ion migration, causing an increase in impedance, and ultimately restricting the improvement of the discharge specific capacity and rate performance of the electrode material; (3) Interfacial side reactions during cycling: During electrochemical cycling, LiOH and the main component of the electrolyte, LiPF6, will undergo a side reaction to generate HF. On the one hand, Li2CO3 reacts with HF to generate CO2, causing the battery to bulge and gas, affecting its cycle performance and safety performance (potential danger of fire and explosion). On the other hand, HF can dissolve the transition metal ions in the ternary cathode material, destroy its layered crystal structure, and deteriorate the thermal stability and rate performance of the electrode material. In addition, high-nickel materials can undergo side reactions with the electrolyte to generate byproducts such as LiF, LiO2, Li2CO3 and LiOH that hinder lithium ion transport, as well as a Ni-O-like resistive layer with Fm-3m rock salt structure, increasing diffusion resistance; (4) Crystal structure phase transformation (degradation): During the sintering preparation and charge-discharge cycle of high-nickel NCM ternary layered cathode material, RLCs are continuously enriched on the surface, continuously aggravating microcracks and Li + / Ni 2+ The degree of mixing and interfacial side reactions; simultaneously, the formation of RLCs is accompanied by the consumption of lattice lithium and lattice oxygen, Ni 3+ The reduction and formation of reactive oxygen species exacerbate the deterioration of the crystal structure; RLCs cause the crystal structure to gradually change from layered R-3m structure to spinel Fd-3m structure or even rock salt phase Fm-3m structure from different angles, resulting in a sharp degradation of the material's electrochemical performance and structural stability; (5) residual alkali insulating layer, the deposited residual alkali layer solidifies the lithium ions and transition metal ions (nickel, cobalt, manganese) on the surface, forming a high impedance layer to inhibit Li + The insertion and extraction of ions reduce the electronic conductivity and ion diffusion rate of the material, leading to increased polarization and deterioration of the electrochemical performance of the electrode material; (6) Slurry gelation occurs during subsequent processing and production. As the surface RLCs increase, the excessive alkalinity causes the viscosity to increase and form a gel during the preparation of the electrode material slurry, resulting in uneven coating and insufficient adhesion, which seriously affects the preparation and coating process of the electrode material and increases production costs. Therefore, it is imperative to take effective strategies to remove residual alkali from the surface of high-nickel ternary electrode materials.

[0004] Currently, modification strategies for removing surface reactive lithium-ion cells (RLCs) from high-nickel NCM ternary layered cathode materials typically include deionized water washing and surface coating. Applying hydrophobic coatings or in-situ bonding with surface RLCs to generate hydrophobic coatings can effectively reduce surface-soluble RLCs and inhibit the corrosion of H2O and CO2 in the air during storage, as well as the side reactions at the electrode material-electrolyte interface during electrochemical cycling. This helps reduce lithium-nickel mixing, suppress phase transitions, and stabilize the material's crystal structure. However, surface coating alone cannot completely remove the residual alkaline insulating layer and reduce surface impedance, thus hindering improvements in electrochemical performance and increasing Li-N-T content. + The ability to embed / de-embed is limited. Deionized water washing is simple, inexpensive, and pollution-free, effectively removing surface-soluble RLCs and is widely used in factories for RLC removal. While deionized water washing utilizes the high solubility of RLCs in deionized water to significantly remove high-alkali impedance layers and substantially improve discharge specific capacity and ion diffusion rate, resulting in excellent removal efficiency, the washing process can easily induce microcrack propagation, intensified cation mixing, structural instability, and erosion from interfacial side reactions during charge and discharge due to the sensitivity of nickel-rich NCM ternary materials to CO2 / H2O in the air. Furthermore, after deionized water washing, the material surface approaches an ideal state, which can significantly exacerbate the harmful phase transition from layered structure (R3m) to disordered spinel-type structure (Fd3m) and rock salt phase structure (Fm3m), reducing the material's structural stability. Therefore, it is difficult to simultaneously improve the material's structural stability, energy density, and rate performance using only surface coating and deionized water washing. Summary of the Invention

[0005] To address the problems of complex processes, high costs, environmental pollution, and poor alkali reduction effects in existing methods for removing residual alkali from the surface of high-nickel ternary electrode materials, the present invention aims to provide a method for reducing residual alkali on the surface of high-nickel ternary electrode materials. This method can significantly enhance the stability and integrity of the material's crystal structure, further improve the cycle stability of high-nickel NCM ternary layered cathode materials, and is simple in process, low in cost, has good alkali reduction effect, is energy-saving and environmentally friendly, and is conducive to commercial promotion and application.

[0006] To achieve the above-mentioned technical objectives, the present invention provides a method for reducing residual alkali on the surface of high-nickel ternary electrode materials. The method involves stirring and washing the high-nickel ternary electrode material with a mixed washing solution containing deionized water and organic long-chain fatty acid solution, followed by solid-liquid separation to obtain a solid product.

[0007] This invention employs a mixed washing solution containing deionized water and an organic long-chain fatty acid solution to wash the surface of high-nickel ternary electrode materials. On one hand, the deionized water rapidly dissolves surface LiOH / Li2CO3, effectively removing soluble reactive carbon ions (RLCs) from the surface of the high-nickel NCM ternary layered cathode material. On the other hand, based on a synergistic coupling effect, while the deionized water rapidly and effectively removes surface-soluble RLCs, the carboxyl groups (-COOH) in the water-immiscible organic long-chain fatty acid molecules react with the residual hydroxyl groups (-OH) adsorbed on the surface of the washed high-nickel ternary electrode material. Chemical bonding occurs, and due to the entanglement of long-chain hydrocarbon groups, the surface of the material is coated with an organic long-chain fatty acid monolayer to form an organic protective layer, thereby improving the hydrophobicity of the material surface. This prevents the high-nickel ternary electrode material from continuing to react with H2O and CO2 in the air to generate LiOH / Li2CO3 during subsequent processing, thus inhibiting and reducing the increase of residual lithium. In addition, the protective layer formed on the surface can inhibit the direct contact between the active material and the electrolyte, prevent the dissolution of transition metal ions, the release of oxygen, and lattice phase transitions, thereby enhancing the stability and integrity of the material's lattice structure.

[0008] As a preferred embodiment, the organic long-chain fatty acid includes at least one selected from stearic acid, lauric acid, oleic acid, palmitic acid, and myristic acid. Using this type of organic long-chain fatty acid can achieve a good alkali-reducing effect.

[0009] As a preferred embodiment, the organic long-chain fatty acid solution uses ethanol as a solvent. Using ethanol as a solvent provides excellent dissolution of organic long-chain fatty acids.

[0010] As a preferred embodiment, the organic long-chain fatty acid solution is obtained by mixing organic long-chain fatty acids and solvent at a mass-volume ratio of 1g:300-500mL.

[0011] Organic long-chain fatty acids, acting as organic surfactants, chemically bond with high-nickel NCM ternary layered cathode materials after washing with deionized water to form a hydrophobic protective layer. The concentration of these fatty acids will affect the lattice structure stability and electrochemical performance of the electrode material after washing and modification. When the concentration of the organic long-chain fatty acid solution is too low, i.e., under a certain mass ratio (deionized water and organic long-chain fatty acid solution), the low proportion of organic long-chain fatty acid solution in the mixed washing solution does not thoroughly and sufficiently coat the washed high-nickel NCM ternary layered cathode material, failing to form a uniform and effective protective layer to prevent the high-nickel ternary electrode material from continuing to react with CO2 and H2O in the air to generate Li2CO3 and LiOH, thus increasing the residual lithium content. When the concentration of the organic long-chain fatty acid solution is too high, i.e., under a certain mass ratio (deionized water and organic long-chain fatty acid solution), the high proportion of organic long-chain fatty acid solution in the mixed washing solution, in addition to forming a uniform coating layer through chemical bonding with the residual hydroxyl groups (-OH) on the electrode material surface, subsequently forms a second physical coating layer with the outer layer of stearic acid and the excess organic long-chain fatty acids in the solution. This results in an excessively thick coating layer, significantly inhibiting charge migration and ion shuttle, and reducing the capacity and rate performance of the electrode material. Therefore, controlling the concentration of the organic long-chain fatty acid solution within a reasonable range is beneficial to improving the lattice structure stability and electrochemical performance of the electrode material.

[0012] As a preferred embodiment, the mass ratio of deionized water to organic long-chain fatty acid solution in the mixed washing liquid is 1:1 to 5.

[0013] Deionized water and organic long-chain fatty acid solution are used as a mixed-phase synergistic modifier for high-nickel NCM ternary layered cathode materials. Controlling the mass ratio of the two within a suitable range can achieve good washing results. If the mass ratio of deionized water to organic long-chain fatty acid solution is too high, the mixed washing solution contains a high proportion of deionized water. While effectively and thoroughly washing away residual lithium on the surface of the high-nickel NCM ternary layered cathode material, this leads to a significant loss of bulk lithium from the electrode material's lattice, exacerbating microcrack propagation, cation mixing, interfacial side reactions, and lattice phase transitions. This significantly reduces the thermal stability of the lattice structure and subsequent electrochemical cycling stability. Furthermore, after washing with a high proportion of deionized water, the residual hydroxyl groups (-OH) on the surface of the high-nickel ternary material are significantly reduced, decreasing the probability of subsequent chemical bonding by organic long-chain fatty acids, resulting in incomplete and insufficient coating. Conversely, if the mass ratio of deionized water to organic long-chain fatty acid solution is too low, the mixed washing solution containing a high proportion of organic long-chain fatty acid solution may lead to an excessively thick high-resistivity coating layer, inhibiting Li... + The insertion and extraction of these substances reduce the electronic conductivity and ion diffusion rate of the material, leading to increased polarization and deterioration of the electrochemical performance of the electrode material. At the same time, a high proportion of organic long-chain fatty acid solutions increases costs and exacerbates environmental pollution.

[0014] As a preferred embodiment, the solid-liquid ratio of the high-nickel ternary electrode material to the mixed washing solution is 1g:1-50mL.

[0015] During the washing process, controlling the solid-liquid ratio of the electrode material to the washing solution within a reasonable range can yield electrode materials with better performance. If the solid-liquid ratio is too high, the solid content in the mixture will be too high, increasing the stirring load and exacerbating the difficulty of stirring. Furthermore, the high-nickel NCM ternary layered cathode material will not have sufficient contact with the washing solution, failing to effectively remove residual alkali from the surface. Simultaneously, the surface coating layer reaction will be uneven and insufficient, thus failing to maximize the synergistic coupling effect of mixed-phase washing. If the solid-liquid ratio is too low, the washing solution content in the mixture will be too high; increasing the amount of deionized water or organic long-chain fatty acid solution will damage the layered structure and cause subsequent over-coating, reducing the lattice structure stability and capacity ratio performance of the electrode material.

[0016] As a preferred embodiment, the stirring and washing conditions are: temperature of 20-50℃, time of 1-30 min, and stirring speed of 100-500 r / min.

[0017] As a preferred approach, the solid product is subjected to washing and drying post-treatment. Washing and drying the solid product removes the washing liquid from its surface.

[0018] As a preferred embodiment, anhydrous ethanol is used as the cleaning agent during the cleaning process.

[0019] As a preferred embodiment, the drying conditions are: vacuum drying, temperature of 100-120℃, and drying time of 8-12 hours.

[0020] Compared with the prior art, the present invention has the following advantages:

[0021] (1) A mixed washing solution containing deionized water and organic long-chain fatty acid solution is used, and a dual modification strategy combining deionized water washing and surface coating is adopted to greatly improve the removal efficiency of residual alkali on the surface of high-nickel ternary electrode material. Based on its synergistic coupling effect, the stability and integrity of the material's crystal structure are significantly enhanced while removing residual alkali on the surface, further improving the cycle stability of high-nickel ternary electrode material.

[0022] (2) Low residual alkali and high nickel ternary electrode materials can be obtained without secondary sintering process, which can significantly reduce reaction energy consumption. Moreover, the alkali reduction method is simple, low cost, and thorough washing.

[0023] (3) The organic long-chain fatty acids in this method can be well separated from deionized water, so that the organic long-chain fatty acids can be recycled and will not cause environmental pollution. It has the advantages of energy saving and environmental protection and can be widely used in the subsequent processing and modification of commercial high-nickel NCM ternary layered cathode materials. Attached Figure Description

[0024] Figure 1 These are scanning electron microscope (SEM) images of the low-alkalinity, high-nickel NCM ternary cathode materials prepared in Examples 1 and Comparative Examples 1-3.

[0025] Figure 2 These are the initial charge-discharge curves of the low-alkalinity, high-nickel NCM ternary cathode materials prepared in Example 1 and Comparative Examples 1-3.

[0026] Figure 3 The graphs show the cycle performance of the low-alkalinity, high-nickel NCM ternary cathode materials prepared in Examples 1 and Comparative Examples 1-3.

[0027] Figure 4 This is a capacity retention diagram of the low-alkalinity, high-nickel NCM ternary cathode materials prepared in Example 1 and Comparative Examples 1-3. Detailed Implementation

[0028] The following examples are intended to further illustrate the present invention, rather than to limit the scope of the claims.

[0029] Example 1

[0030] The following is the first method for reducing residual alkali on the surface of high-nickel ternary electrode materials, including the following steps:

[0031] (1) Add 0.1g stearic acid to 50mL anhydrous ethanol solution and stir well; then mix 25ml deionized water and 50ml stearic acid alcohol solution (1:2) and stir well to prepare washing solution;

[0032] (2) Select chemical composition LiNi 0.8 Co 0.1 Mn 0.1 Commercial high-nickel LNCM ternary layered cathode material of O2 was used as the material to be washed. According to the solid-liquid ratio of 1:10, that is, 5g of high-nickel LNCM ternary material was dissolved in 50mL of washing solution and quickly placed in a water bath for stirring and washing. The speed was set to 200rpm / min, the stirring time was 5min, and the washing temperature was 35℃.

[0033] (3) The slurry that has been stirred and washed for 5 minutes is quickly transferred to a circulating water multi-purpose vacuum pump for filtration. Then the material obtained by filtration is transferred to a vacuum drying oven and dried at 100°C for 12 hours to obtain a high-nickel ternary layered cathode material with low residual alkali.

[0034] Example 2

[0035] The following is a second method for reducing residual alkali on the surface of high-nickel ternary electrode materials, including the following steps:

[0036] (1) Add 0.1g of lauric acid to 50mL of anhydrous ethanol solution and stir well; then mix 25ml of deionized water and 50ml of lauric acid alcohol solution (1:2) and stir well to prepare the washing solution;

[0037] (2) Select chemical composition LiNi 0.8 Co 0.1 Mn 0.1 Commercial high-nickel LNCM ternary layered cathode material of O2 was used as the material to be washed. According to the solid-liquid ratio of 1:10, that is, 5g of high-nickel LNCM ternary material was dissolved in 50mL of washing solution and quickly placed in a water bath for stirring and washing. The speed was set to 200rpm / min, the stirring time was 5min, and the washing temperature was 35℃.

[0038] (3) The slurry that has been stirred and washed for 5 minutes is quickly transferred to a circulating water multi-purpose vacuum pump for filtration. Then the material obtained by filtration is transferred to a vacuum drying oven and dried at 100°C for 12 hours to obtain a high-nickel ternary layered cathode material with low residual alkali.

[0039] Example 3

[0040] The following is the third method for reducing residual alkali on the surface of high-nickel ternary electrode materials, including the following steps:

[0041] (1) Add 0.1g of oleic acid to 50mL of anhydrous ethanol solution and stir until homogeneous; then mix 25mL of deionized water and 50mL of oleic acid alcohol solution (1:2) and stir until homogeneous to prepare the washing solution;

[0042] (2) Select chemical composition LiNi 0.8 Co 0.1 Mn 0.1 Commercial high-nickel LNCM ternary layered cathode material of O2 was used as the material to be washed. According to the solid-liquid ratio of 1:10, that is, 5g of high-nickel LNCM ternary material was dissolved in 50mL of washing solution and quickly placed in a water bath for stirring and washing. The speed was set to 200rpm / min, the stirring time was 5min, and the washing temperature was 35℃.

[0043] (3) The slurry that has been stirred and washed for 5 minutes is quickly transferred to a circulating water multi-purpose vacuum pump for filtration. Then the material obtained by filtration is transferred to a vacuum drying oven and dried at 100°C for 12 hours to obtain a high-nickel ternary layered cathode material with low residual alkali.

[0044] Example 4

[0045] The following is the fourth method for reducing residual alkali on the surface of high-nickel ternary electrode materials, including the following steps:

[0046] (1) Add 0.1g palmitic acid to 50mL of anhydrous ethanol solution and stir well; then mix 25ml of deionized water and 50ml of palmitic acid alcohol solution (1:2) and stir well to prepare washing solution;

[0047] (2) Select chemical composition LiNi 0.8 Co 0.1 Mn 0.1 Commercial high-nickel LNCM ternary layered cathode material of O2 was used as the material to be washed. According to the solid-liquid ratio of 1:10, that is, 5g of high-nickel LNCM ternary material was dissolved in 50mL of washing solution and quickly placed in a water bath for stirring and washing. The speed was set to 200rpm / min, the stirring time was 5min, and the washing temperature was 35℃.

[0048] (3) The slurry that has been stirred and washed for 5 minutes is quickly transferred to a circulating water multi-purpose vacuum pump for filtration. Then the material obtained by filtration is transferred to a vacuum drying oven and dried at 100°C for 12 hours to obtain a high-nickel ternary layered cathode material with low residual alkali.

[0049] Example 5

[0050] The following is the fifth method for reducing residual alkali on the surface of high-nickel ternary electrode materials, including the following steps:

[0051] (1) Add 0.1g myristic acid to 50mL of anhydrous ethanol solution and stir well; then mix 25ml of deionized water and 50ml of myristic acid alcohol solution (1:2) and stir well to prepare the washing solution;

[0052] (2) Select chemical composition LiNi 0.8 Co 0.1 Mn 0.1 Commercial high-nickel LNCM ternary layered cathode material of O2 was used as the material to be washed. According to the solid-liquid ratio of 1:10, that is, 5g of high-nickel LNCM ternary material was dissolved in 50mL of washing solution and quickly placed in a water bath for stirring and washing. The speed was set to 200rpm / min, the stirring time was 5min, and the washing temperature was 35℃.

[0053] (3) The slurry that has been stirred and washed for 5 minutes is quickly transferred to a circulating water multi-purpose vacuum pump for filtration. Then the material obtained by filtration is transferred to a vacuum drying oven and dried at 100°C for 12 hours to obtain a high-nickel ternary layered cathode material with low residual alkali.

[0054] Comparative Example 1

[0055] The chemical composition was chosen as LiNi.0.8 Co 0.1 Mn 0.1 Using commercially available high-nickel LNCM ternary layered cathode material as the material to be washed, 5g of high-nickel LNCM ternary material was dissolved in 50mL of deionized water and quickly placed in a water bath for stirring and washing. The stirring speed was set to 200rpm / min, the stirring time to 5min, and the washing temperature to 35℃. The slurry after 5min of stirring and washing was quickly transferred to a circulating water multi-purpose vacuum pump for filtration. Then, the material obtained by filtration was transferred to a vacuum drying oven and dried at 100℃ for 12h to obtain high-nickel ternary layered cathode material with low residual alkali.

[0056] Comparative Example 2

[0057] The chemical composition was chosen as LiNi. 0.8 Co 0.1 Mn 0.1 Using commercially available high-nickel LNCM ternary layered cathode material as the material to be washed, 5g of high-nickel LNCM ternary material was dissolved in 50mL of anhydrous ethanol solution and quickly placed in a water bath for stirring and washing. The stirring speed was set to 200rpm / min, the stirring time to 5min, and the washing temperature to 35℃. The slurry after 5min of stirring and washing was quickly transferred to a circulating water multi-purpose vacuum pump for filtration. Then, the material obtained by filtration was transferred to a vacuum drying oven and dried at 100℃ for 12h to obtain high-nickel ternary layered cathode material with low residual alkali.

[0058] Comparative Example 3

[0059] The method of Example 1 was used to prepare a high-nickel ternary layered cathode material with low residual alkali, except that deionized water was not added during the preparation of the washing solution.

[0060] Lithium content test: The lithium content of the filtrates obtained from Examples 1-5 and Comparative Examples 1-3 after filtration was tested. Specifically, inductively coupled plasma optical emission spectrometry (ICP) was used to analyze the Li content in the washing liquid (filtrate). + The content was tested, and the results are shown in Table 1:

[0061] Table 1

[0062]

[0063]

[0064] As shown in Table 1, Examples 1-5 and Comparative Example 1, after being washed with a small amount of deionized water, can significantly remove soluble RLCs from the surface of the high-nickel NCM ternary electrode material and reduce the amount of residual lithium on the surface. However, in Comparative Examples 2-3, due to the slightly soluble nature of Li2CO3, washing with a single anhydrous ethanol and organic long-chain fatty acid ethanol solution has limitations in removing residual alkali from the surface and cannot quickly and effectively remove the residual alkali impedance layer.

[0065] SEM testing: The morphology of the low-alkali, high-nickel NCM ternary layered cathode materials prepared in Example 1 and Comparative Examples 1-3 was observed using SEM to investigate the influence of different washing processes on their morphological structure. Figure 1 As shown, the electrode material obtained in Example 1 is coated with a uniform long-chain stearic acid layer, indicating that the initial washing with a small amount of deionized water can effectively remove the surface RLCs (-OH in LiOH / Li2CO3). During the subsequent stirring and washing process, the carboxyl groups (-COOH) in the stearic acid molecules can form chemical bonds with the residual hydroxyl groups (-OH) adsorbed on the surface of the high-nickel NCM ternary layered cathode material, forming a uniform organic coating layer. The electrode material obtained in Comparative Example 1 has clear and complete grain boundaries, and the surface residual alkali is completely removed, further demonstrating the advantage of deionized water washing in removing residual alkali from the surface of high-nickel ternary electrode materials. The electrode material obtained in Comparative Example 2... Due to the slight solubility of Li2CO3 in anhydrous ethanol, the removal effect of residual alkali on the surface is poor. It can be observed that a large amount of unwashed residual alkali remains on the surface, which seriously affects the stability of the crystal structure and the improvement of electrochemical performance. The electrode material obtained in Comparative Example 3 has an excessively thick stearic acid layer and residual alkali layer on its surface because the ethanol solution of stearic acid cannot effectively and completely remove the residual alkali on the surface. The carboxyl group (-COOH) in the stearic acid molecule not only bonds with the residual hydroxyl group (-OH) adsorbed on the surface of the high-nickel NCM ternary layered cathode material, but also chemically associates with a large amount of LiOH / Li2CO3 (-OH) remaining on the surface, resulting in an excessively thick high-resistivity coating layer, which seriously reduces electron charge transport and ion shuttle.

[0066] Electrochemical performance testing: The low-alkali, high-nickel NCM ternary layered cathode materials obtained in Examples 1-5 and Comparative Examples 1-3, conductive carbon black, and PVDF were mixed in a mass ratio of 8 / 1 / 1 and stirred in NMP until a uniform slurry was formed. This slurry was then uniformly coated onto aluminum foil using a coating machine and dried in a vacuum drying oven at 100°C for 12 hours. The aluminum foil loaded with electrode active materials was then uniformly cut into electrode sheets with a diameter of 12 mm. In a glove box filled with high-purity argon, using the cut electrode aluminum foil as the working electrode, lithium metal as the counter electrode, and Celgard 2500 as the separator, a CR2016 coin cell was assembled. The electrochemical performance of the assembled lithium-ion battery was then tested using a blue-light electrochemical analyzer, as detailed below:

[0067] First charge-discharge test: Lithium-ion coin cells prepared with the low-alkali, high-nickel NCM ternary layered cathode materials of Examples 1-5 and Comparative Examples 1-3 were charged and discharged at a voltage range of 2.8-4.5V with a charge-discharge ratio of 0.04A g. -1 The current density was used for charging and discharging to obtain the first charge-discharge curves and capacity, and the results are shown in Table 2 below:

[0068] Table 2

[0069]

[0070] As shown in Table 2, washing with deionized water can effectively remove the residual alkali impedance layer on the material surface, significantly improving electronic conductivity and ion diffusion rate, which is beneficial to improving discharge specific capacity and coulombic efficiency. However, washing with a single anhydrous ethanol and organic long-chain fatty acid alcohol solution not only fails to effectively remove the residual alkali impedance layer on the surface, but also forms an excessively thick coating layer with the residual alkali through chemical bonding, resulting in a large impedance value. This affects the improvement of electronic conductivity and lithium ion diffusion rate, leading to lower first-round discharge specific capacity and coulombic efficiency.

[0071] Cycle performance testing: Lithium-ion coin cells prepared with the low-alkali, high-nickel NCM ternary layered cathode materials of Examples 1-5 and Comparative Examples 1-3 were subjected to cycling tests at 0.2 A g. -1 The reversible capacity and capacity retention rate after 50 cycles were obtained by conducting 50 charge-discharge cycles at the current density. The results are shown in Table 3 below.

[0072] Table 3

[0073]

[0074]

[0075] As shown in Table 3, in Examples 1-5, the deionized water washing in the mixed washing solution effectively removes the residual alkali impedance layer on the electrode material surface, improving the initial discharge specific capacity and coulombic efficiency. Simultaneously, the chemical bonding of organic long-chain fatty acids forms a coating layer, effectively preventing the electrode material from continuing to react with H2O and CO2 in the air to generate LiOH / Li2CO3 and avoiding side reactions at the electrolyte interface during subsequent drying and utilization. This significantly improves the thermal stability of the crystal structure and the electrochemical cycle stability. In contrast, in Comparative Example 1, while deionized water washing alone effectively removes residual alkali from the surface, it exacerbates the reaction with CO2 / H2 in the air during subsequent drying and processing of the nickel-rich NCM ternary material after washing. The sensitive effect of O easily causes microcrack propagation, intensified cation mixing, structural instability, and erosion by interfacial side reactions during charging and discharging. In addition, after washing with deionized water, the material surface is close to an ideal state, which can significantly aggravate the harmful phase transition from layered structure (R3m) to disordered spinel-type structure (Fd3m) and rock salt phase structure (Fm3m), reducing the structural stability of the material. In comparative examples 2 and 3, washing with alcohol solutions of anhydrous ethanol and organic long-chain fatty acids alone cannot effectively remove residual alkali from the surface. The presence of residual alkali aggravates material instability phenomena such as microcrack propagation, cation mixing, interfacial side reactions, lattice lithium dissolution, and lattice phase transition, seriously damaging the material's lattice structure and affecting the improvement of electrochemical cycling performance.

[0076] To further illustrate the advantages of the present invention, Figures 2-4 The diagrams provide a more intuitive and clear view of the first charge-discharge curves, cycle performance graphs, and capacity retention rate graphs for Example 1 and Comparative Examples 1-3.

[0077] The above description is merely a preferred embodiment of the present invention and is a further detailed description of the present invention in conjunction with specific preferred embodiments. It should not be construed that the specific implementation of the present invention is limited to these descriptions. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for reducing residual alkali on the surface of a high-nickel ternary electrode material, characterized in that: The high-nickel ternary electrode material was stirred and washed with a mixed washing solution containing deionized water and organic long-chain fatty acid solution, and the solid-liquid separation was performed to obtain a solid product. The organic long-chain fatty acid solution uses ethanol as a solvent; The organic long-chain fatty acid solution is obtained by mixing organic long-chain fatty acids and solvent at a mass-volume ratio of 1g:300~500mL; The mass ratio of deionized water to organic long-chain fatty acid solution in the mixed washing solution is 1:1~5; The organic long-chain fatty acids include at least one of stearic acid, lauric acid, oleic acid, palmitic acid, and myristic acid.

2. The method for reducing residual alkali on the surface of a high-nickel ternary electrode material according to claim 1, characterized in that: The solid-liquid ratio of the high-nickel ternary electrode material to the mixed washing solution is 1g:1~50mL.

3. A method for reducing residual alkali on the surface of a high-nickel ternary electrode material according to claim 1 or 2, characterized in that: The stirring and washing conditions are: temperature 20~50℃, time 1~30min, and stirring speed 100~500r / min.

4. The method for reducing residual alkali on the surface of a high-nickel ternary electrode material according to claim 1, characterized in that: Solid products are then cleaned, dried, and processed.

5. The method for reducing residual alkali on the surface of a high-nickel ternary electrode material according to claim 4, characterized in that: Anhydrous ethanol is used as the cleaning agent in the cleaning process.

6. A method for reducing residual alkali on the surface of a high-nickel ternary electrode material according to claim 4 or 5, characterized in that: The drying conditions are: vacuum drying, temperature of 100~120℃, and drying time of 8~12h.

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