Surface treatment method for improving cycle stability of high-voltage cathode material

Abstract

The application discloses a surface treatment method for improving cycle stability of high-voltage positive electrode materials, and relates to the technical field of lithium ion battery positive electrode materials, and comprises the following steps: high-voltage positive electrode material powder is pretreated in a weak acid or an amino carboxylic complexing agent aqueous solution with pH 3-6 at 50-70 DEG C for 1-2 hours, then after washing and drying, the high-voltage positive electrode material is immersed in a precursor solution containing a metal source and a carbon source, and then is subjected to heat preservation at 300-500 DEG C in an oxidizing atmosphere for 2-4 hours to form a composite coating layer, and finally is subjected to heat preservation at 600-750 DEG C in an inert atmosphere for 1-2 hours, so that the high-voltage positive electrode material with cycle stability is obtained; the surface treatment method for improving cycle stability of high-voltage positive electrode materials can accurately remove surface inert residual lithium compounds through mild pretreatment of a weak acid or a complexing agent, expose transition metal active sites, lay a foundation for formation of a subsequent coating layer and in-situ M-O-M' chemical bonds, greatly enhance the interface bonding strength of the coating layer and the matrix, and avoid peeling in the cycle process.

Description

Technical Field

[0001] This invention relates to lithium-ion battery cathode material technology, specifically to a surface treatment method for improving the cycle stability of high-voltage cathode materials. Background Technology

[0002] To achieve higher energy density, the operating voltage is developed to be no less than 4.5V (relative to Li). + High-voltage cathode materials (such as high-voltage lithium cobalt oxide, high-nickel ternary materials, and lithium-rich manganese-based lattice materials) have become an important research direction.

[0003] However, these materials face severe challenges when cycling at high voltages: the severe oxidative decomposition of the electrolyte under high voltage leads to a surge in interfacial impedance and loss of active materials; residual lithium compounds (such as Li2CO3 and LiOH) on the material surface react with the electrolyte, causing problems such as gas generation and pulverization; during the high-voltage cycling process of repeated lithium ion insertion and extraction, the material undergoes irreversible phase transitions and dissolution of transition metal ions, resulting in structural collapse and capacity decay.

[0004] Surface coating technology is often used to improve interface stability, but traditional coatings (such as single metal oxides or carbon layers) have the following shortcomings: single metal oxide coatings have poor conductivity and weak adhesion to the substrate, and are easy to peel off during long-term cycling; single carbon layers can improve conductivity, but their physical barrier and chemical anchoring effect against electrolyte corrosion is limited. Summary of the Invention

[0005] The purpose of this invention is to provide a surface treatment method to improve the cycle stability of high-voltage cathode materials, thereby solving the problem of poor cycle stability of high-voltage cathode materials.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a surface treatment method for improving the cycle stability of high-voltage cathode materials, comprising the following steps:

[0007] S1. Place the high-voltage cathode material powder in a weakly acidic aqueous solution with a pH of 3-6 or an aqueous solution containing an aminocarboxylic acid complexing agent, and perform surface pretreatment at 50-70℃ for 1-2 hours. Then wash and dry to obtain the treated cathode material.

[0008] S2. The treated cathode material is immersed in a homogeneous precursor mixture solution containing a metal source and a carbon source to obtain the immersed material.

[0009] S3. The impregnated material is heated to 300-500℃ in an oxidizing atmosphere and kept at this temperature for 2-4 hours to form a composite coating layer on the surface of the high voltage cathode material particles, thereby obtaining the modified material.

[0010] S4. Under an inert atmosphere, the modified material is heated to 600-750℃ and held for 1-2 hours to obtain a cycle-stable high-voltage cathode material.

[0011] Furthermore, the high-voltage cathode material described in S1 is high-voltage lithium cobalt oxide with the general chemical formula LiNi. x Co y Mn z O2-rich high-nickel ternary materials or lithium-rich manganese-based lattice materials with reversible anionic redox reactions.

[0012] Furthermore, the general chemical formula is LiNi. x Co y Mn z O2 high-nickel ternary material, where x≥0.6 and x+y+z=1.

[0013] Furthermore, the weakly acidic aqueous solution described in S1 is dilute acetic acid, dilute citric acid, or a carbon dioxide-saturated aqueous solution.

[0014] Furthermore, the metal source in S2 is an alkoxide or organic acid salt of aluminum, zirconium, or titanium, and the carbon source in S2 is sucrose, glucose, citric acid, or polyethylene glycol.

[0015] Furthermore, the alkoxide is aluminum isopropoxide, tetrabutyl titanate, or tetrabutyl zirconate; the organic acid salt is acetate or citrate.

[0016] Furthermore, the thickness of the composite coating layer described in S3 is 5-30 nm.

[0017] Furthermore, the heating rate to 600-750°C described in S4 is 3-10°C / min.

[0018] Furthermore, the heating rate of S3 to 300-500℃ is 2-5℃ / min.

[0019] A high-voltage cathode material is prepared by the surface treatment method described above for improving the cycle stability of high-voltage cathode materials.

[0020] Compared with the prior art, the present invention provides a surface treatment method to improve the cycle stability of high voltage cathode materials. Through mild pretreatment with weak acid or complexing agent, the surface inert residual lithium compounds are precisely removed, and the transition metal active sites are exposed. This lays the foundation for the subsequent formation of the coating layer and in-situ MO-M' chemical bonds, greatly enhances the interfacial bonding strength between the coating layer and the substrate, and avoids peeling during cycling.

[0021] Through precursor solution impregnation and programmed temperature pyrolysis, a unique composite structure of metal oxide nanoparticles embedded in an amorphous carbon matrix was formed in situ. The amorphous carbon network provides a continuous electronic conduction path, significantly improving interfacial charge transport; the uniformly dispersed metal oxide nanoparticles act as a physical barrier, effectively inhibiting the erosion of the cathode material by the electrolyte and the dissolution of transition metals, and enhancing structural stability.

[0022] This composite coating combines the chemical stability of metal oxides with the excellent electrical conductivity of carbon materials. The two work synergistically to construct an ideal interface that combines high ionic / electronic conductivity, excellent mechanical strength, and strong interfacial chemical bonding. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this invention. For those skilled in the art, other drawings can be obtained based on these drawings.

[0024] Figure 1 This is a schematic diagram of the overall process of the surface treatment method provided in an embodiment of the present invention. Detailed Implementation

[0025] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.

[0026] Example 1:

[0027] Please see Figure 1 A surface treatment method for improving the cycle stability of high-voltage cathode materials includes the following steps:

[0028] S1, Take 10 grams of commercial LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811) cathode material powder (operating voltage up to 4.5V) was dispersed in 100 mL of dilute acetic acid aqueous solution with a pH of 4.0 and stirred in a 60°C water bath for 1.5 hours. After the reaction, the powder was repeatedly washed with deionized water by centrifugation until the filtrate was neutral, and then dried in a 120°C vacuum oven for 12 hours to obtain pretreated NCM811 powder. This step effectively removed Li2CO3 and LiOH from the surface.

[0029] NCM811 powder, as a high-voltage cathode material matrix, has high specific capacity and working voltage potential of over 4.5V, making it a core substrate for meeting high energy density requirements. However, residual lithium compounds (Li2CO3, LiOH) are easily formed on its surface, which restricts cycle stability.

[0030] A weakly acidic system of dilute acetic acid aqueous solution (pH=4.0) is the key medium for residual lithium removal. Through a mild acid-base reaction (Li₂CO₃ + 2CH₃COOH = 2CH₃COOLi + CO₂ + H₂O, LiOH + CH₃COOH = CH₃COOLi + H₂O), it precisely removes inert residual lithium from the surface, avoiding the corrosion of the NCM811 layered structure by strong acid solutions. Simultaneously, the generated lithium acetate is readily soluble in water and can be completely removed by washing. pH=4.0 is the optimal weakly acidic range; when pH>4, the H₂ from the ionization of dilute acetic acid... + Insufficient concentration results in low residual lithium removal efficiency, leaving Li2CO3 / LiOH residues on the surface; when pH < 4, the acidity is too strong, which will corrode the transition metal oxides on the NCM811 surface, leading to material structural damage and capacity loss.

[0031] Deionized water is used to wash away residual acetic acid, lithium acetate, and other impurities, preventing these residues from affecting the subsequent bonding between the coating layer and the substrate. A liquid-to-solid ratio (100mL:10g) ensures that the NCM811 powder is fully dispersed in the solution, allowing each particle to contact dilute acetic acid and preventing localized particle agglomeration that could lead to incomplete lithium removal. A 60℃ water bath temperature increases the acid-base reaction kinetics and shortens the lithium removal time; below 50℃, the reaction rate is too slow, and lithium residue cannot be completely removed within 1.5 hours; above 70℃, dilute acetic acid is volatile, causing an increase in the solution pH and potentially leading to slight dissolution of the NCM811 surface.

[0032] A 1.5-hour processing time ensures sufficient reaction between the residual lithium compound and dilute acetic acid. Insufficient time results in incomplete removal of residual lithium, while excessive time increases the risk of dissolution of transition metals on the NCM811 surface. Vacuum drying at 120℃ for 12 hours thoroughly removes adsorbed moisture and residual acetic acid from the particle surface. The vacuum environment prevents CO2 and H2O in the air from reacting with the material surface and regenerating residual lithium. 120℃ is the optimal temperature for moisture removal; below 100℃, moisture removal is incomplete, and above 150℃ may cause slight distortion of the material surface structure.

[0033] S2. Immerse the pretreated NCM811 powder in a homogeneous precursor solution. The precursor solution is prepared by dissolving the following components in 50 mL of anhydrous ethanol: 0.2 g of aluminum isopropoxide (as an aluminum source), 0.5 g of sucrose (as a carbon source), and acetylacetone as a stabilizer. Stir and impregnate for 4 hours to ensure the solution fully wets the particle surface. Then, slowly evaporate the solvent at 80°C until dry to obtain the impregnated material.

[0034] Aluminum isopropoxide, as the metal source, can be pyrolyzed to generate Al₂O₃ nanoparticles. Al₂O₃ possesses excellent chemical stability and mechanical strength, and can act as a physical barrier to inhibit electrolyte corrosion and the dissolution of transition metal ions. Sucrose, as the carbon source, forms an amorphous carbon network after carbonization, exhibiting high conductivity, which can improve the electron transport efficiency of the coating layer and compensate for the poor conductivity of single metal oxides. Acetylacetone, as a stabilizer, reacts with the Al in aluminum isopropoxide... 3+ The formation of a complex inhibits the premature hydrolysis of aluminum isopropoxide in anhydrous ethanol to form Al(OH)3 precipitate, ensuring the homogeneity of the precursor solution and thus guaranteeing the uniformity of the subsequent coating layer. Anhydrous ethanol, as a solvent, has good solubility, simultaneously dissolving aluminum isopropoxide, sucrose, and acetylacetone, and has a low volatilization temperature with no residue, avoiding the introduction of other impurities. If water is used as a solvent, aluminum isopropoxide is prone to rapid hydrolysis, leading to precursor aggregation.

[0035] The optimal ratio of aluminum isopropoxide (0.2g) to sucrose (0.5g) ensures the best mass ratio of Al2O3 nanoparticles to amorphous carbon after subsequent pyrolysis (approximately 1:2), guaranteeing both the physical barrier properties of the coating (Al2O3) and the conductivity requirements (amorphous carbon). Excessive aluminum source leads to insufficient carbon network coverage and decreased conductivity; excessive carbon source results in an overly thick coating, affecting lithium-ion transport. 50mL of anhydrous ethanol ensures complete dissolution of the raw materials and full immersion of the NCM811 powder in the solution, preventing excessively high precursor concentration and uneven adsorption due to insufficient solvent. A 4-hour immersion time allows the precursors (aluminum isopropoxide-acetylacetone complex, sucrose) to fully adhere to the NCM811 particle surface through physical adsorption and intermolecular forces. Insufficient time results in insufficient precursor adsorption and an inadequate coating thickness; excessive time provides no additional benefit and increases experimental costs. Slow evaporation at 80℃ avoids rapid solvent evaporation, which can cause precursors to aggregate and clump on the particle surface, ensuring that the precursors are evenly distributed on the particle surface and laying the foundation for the subsequent formation of a uniform composite coating layer. When the evaporation temperature is higher than 90℃, the solvent evaporates too quickly, which can easily lead to precursor agglomeration. When the temperature is lower than 70℃, the evaporation efficiency is low and may cause the precursors to redissolve or migrate.

[0036] S3. The impregnated material is transferred to a tube furnace and heated to 400°C at a rate of 3°C / min under air atmosphere, and held for 3 hours to obtain the modified material. During this process, sucrose carbonizes to form an amorphous carbon network, aluminum isopropoxide decomposes to generate Al2O3, and combines with Ni / Co / Mn atoms on the surface of NCM811 through Al-O-M' chemical bonds, thereby forming a composite coating layer on the surface of NCM811 particles with Al2O3 nanoparticles (approximately 10 nm in size) embedded in the amorphous carbon matrix. The coating layer thickness is approximately 15 nm.

[0037] An air atmosphere provides the oxygen needed for sucrose carbonization (sucrose → amorphous carbon + CO2 + H2O), while also promoting the decomposition of aluminum isopropoxide (Al(OC3H7)3 → Al2O3 + C3H8O). If an inert atmosphere is used, sucrose cannot be carbonized and can only form an organic carbon film, which has poor stability and conductivity.

[0038] A heating rate of 3℃ / min allows for gradual dehydration and carbonization of sucrose, and gradual decomposition of aluminum isopropoxide. This avoids rapid temperature increases that could lead to rapid decomposition of the precursor, generating gas and causing the coating layer to crack and peel off. A heating rate that is too fast (>5℃ / min) will result in an uneven coating layer, while a rate that is too slow (<2℃ / min) will prolong the experimental period and reduce efficiency. A pyrolysis temperature of 400℃ is the optimal synergistic temperature for sucrose carbonization and aluminum isopropoxide decomposition: below 300℃, sucrose carbonization is incomplete (resulting in residual organic impurities), and aluminum isopropoxide decomposition is incomplete; above 500℃, amorphous carbon is easily over-oxidized (generating CO2), leading to a discontinuous carbon network, and simultaneously, Al2O3 particles tend to agglomerate and grow, affecting the coating layer performance. A 3-hour holding time ensures complete carbonization of sucrose, forming an amorphous carbon network, and complete decomposition of aluminum isopropoxide to generate Al2O3. Al2O3 then tightly bonds with Ni / Co / Mn atoms on the NCM811 surface through Al-O-M' chemical bonds (M'=Ni / Co / Mn), enhancing the interfacial bonding between the coating layer and the substrate and preventing coating layer peeling during cycling. Insufficient holding time results in incomplete reaction and an unstable coating layer structure. A 50 mL / min air flow rate promptly removes gases such as CO2, H2O, and isopropanol generated during pyrolysis, preventing gas accumulation in the tubular furnace and affecting the reaction; simultaneously, it ensures a stable oxygen concentration within the furnace, guaranteeing uniform carbonization and decomposition reactions.

[0039] S4. The modified material is heated to 650℃ at 5℃ / min under an argon atmosphere and held for 1.5 hours to further optimize the graphitization degree of carbon and the crystallinity of Al2O3 nanocrystals, improve the overall conductivity and stability of the coating layer, and obtain a cycle-stable high-voltage cathode material, labeled as material A.

[0040] Argon atmosphere isolates the material from air, preventing the NCM811 matrix from being oxidized at high temperatures and also preventing the amorphous carbon from being further oxidized and consumed; if air is used, impurity oxides will be generated on the material surface and the carbon network will be destroyed.

[0041] A heating rate of 5℃ / min balances annealing efficiency and structural stability. Rapid heating shortens experimental time and prevents cracking due to a mismatch in the thermal expansion coefficients of the coating layer and the substrate caused by a sudden temperature rise (the difference in thermal expansion coefficients between Al2O3 and NCM811 is relatively small). An annealing temperature of 650℃ optimizes two key properties: increasing the graphitization degree of amorphous carbon (partially transforming it into a graphite-like structure), reducing electron transport resistance; and promoting the crystallization of Al2O3 nanocrystals (from amorphous to γ-Al2O3), enhancing the mechanical strength and chemical stability of the coating layer. Below 600℃, graphitization and crystallization effects are not significant; above 750℃, Al2O3 particles grow excessively (>20nm), leading to increased porosity of the coating layer, decreased physical barrier properties, and potentially causing lithium insertion / extraction disorder in the NCM811 substrate.

[0042] A 1.5-hour holding time ensures sufficient graphitization and crystallization. Insufficient time leads to incomplete performance optimization, while excessive time results in Al2O3 particle agglomeration and over-graphitization of the carbon network (increasing brittleness). An argon flow rate of 50 mL / min ensures a stable inert environment within the furnace and promptly removes any remaining trace gases (such as CO2 not completely removed from S3) to prevent impurities from affecting material properties.

[0043] Example 2:

[0044] This embodiment provides a technical solution based on Embodiment 1: a surface treatment method for improving the cycle stability of high-voltage cathode materials, comprising the following steps:

[0045] S1. Take 10 grams of high-voltage lithium cobalt oxide (LiCoO2, working voltage 4.6V) powder, disperse it in a carbon dioxide saturated aqueous solution (pH=5.5), treat it at 55℃ for 2 hours, and then wash and dry it to obtain the treated cathode material. This method utilizes the weak acidity of carbonic acid to remove residual lithium more gently.

[0046] S2. Preparation of precursor solution: Dissolve 0.15 g of zirconium acetate (as zirconium source) and 0.6 g of glucose (as carbon source) in a mixed solvent of ethylene glycol and water. Add the treated cathode material powder, ultrasonically disperse and stir for 3 hours, then remove the solvent by rotary evaporation to obtain the impregnated material.

[0047] S3. Place the impregnated material in a flowing oxygen atmosphere, heat it to 350℃ at a rate of 2℃ / min, and hold it for 4 hours to obtain the modified material. Glucose carbonizes to form amorphous carbon, zirconium acetate decomposes to generate ZrO2, and forms Zr-O-Co bonds with Co atoms on the surface of LiCoO2 to generate a ZrO2-amorphous carbon composite coating layer with a thickness of about 10nm, wherein the ZrO2 particle size is about 8nm.

[0048] S4. Under a nitrogen atmosphere, the temperature is increased to 700℃ at 8℃ / min and held for 1 hour to obtain a cycle-stable high-voltage cathode material, which is labeled as material B.

[0049] Example 3:

[0050] This embodiment provides a technical solution based on Embodiment 1: a surface treatment method for improving the cycle stability of high-voltage cathode materials, comprising the following steps:

[0051] S1. Take 10 grams of lithium-rich manganese-based matrix material (Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2 powder was dispersed in an aqueous solution containing 0.05 M ethylenediaminetetraacetic acid (EDTA, an aminocarboxylic acid complexing agent) and treated at 70°C for 1 hour. EDTA can effectively complex residual lithium ions and some transition metal ions on the surface, deeply cleaning the surface. After washing and drying, the treated cathode material was obtained.

[0052] S2. Preparation of precursor solution: 0.18 g of tetrabutyl titanate (as titanium source) and 0.8 g of citric acid (as carbon source and complexing agent) are dissolved in ethanol. The treated cathode material is added and impregnated for 5 hours, followed by drying at 60°C to obtain the impregnated material.

[0053] S3. Under air atmosphere, the impregnated material is heated to 450℃ at a rate of 5℃ / min and held for 2 hours to obtain the modified material. Citric acid decomposes to form an amorphous carbon network, and tetrabutyl titanate decomposes to generate TiO2, which forms Ti-O-M' bonds with Mn / Ni atoms on the material surface, resulting in a TiO2-amorphous carbon composite coating layer with a thickness of approximately 20-25nm, wherein the TiO2 nanoparticles are approximately 15nm in size.

[0054] S4. Under an inert atmosphere, the modified material is heated to 600℃ and held for 1 hour to obtain a cycle-stable high-voltage cathode material, which is labeled as material C.

[0055] Example 4:

[0056] This embodiment provides a technical solution based on Embodiment 1, Embodiment 2 and Embodiment 3: a performance testing experiment of a high-voltage cathode material with stable cycle operation.

[0057] The test samples are as follows: Control group CK1 is the original commercial NCM811 material; Control group CK2 is the original commercial high-pressure LiCoO2 material; Control group CK3 is the original lithium-rich manganese base layer material; Experimental group 1 is material A; Experimental group 2 is material B; Experimental group 3 is material C.

[0058] The above test samples were mixed at a mass ratio of "test sample: conductive carbon black: PVDF = 8:1:1", and NMP was added to form a uniform slurry. This slurry was then coated onto an aluminum foil current collector (coating thickness 100μm). After infrared drying at 80℃ for 2 hours, it was dried in a vacuum oven at 120℃ for 12 hours to remove residual solvent. The dried electrode sheets were then cut into 14mm diameter rounds using a die-cutting machine, with the compaction density controlled at 3.2-3.4g / cm³. 3 The active material loading of the monopolar plate is approximately 2.0 mg / cm³. 2 Thus, a positive electrode sheet is obtained;

[0059] CR2032 coin cell half-cells were assembled in an argon-atmosphere glove box (O2 content < 0.1 ppm, H2O content < 0.1 ppm). The assembly sequence was as follows: positive electrode shell → prepared positive electrode sheet → Celgard 2400 polypropylene separator → addition of 100 μL electrolyte (1 mol / L LiPF6-EC:DMC:EMC volume ratio 1:1:1) → lithium metal sheet (as counter electrode) → gasket → spring sheet → negative electrode shell. A coin cell sealing machine was used to seal the cells at 800 kgf pressure to ensure good battery sealing (no electrolyte leakage). After assembly, the cells were left to stand in the glove box for 24 hours to allow the electrolyte to fully wet the positive electrode sheet and separator, ensuring unobstructed ion transport channels, followed by electrochemical performance testing.

[0060] The electrochemical performance tests are as follows:

[0061] 1. Cyclic stability test:

[0062] The LAND CT2001A charge-discharge tester was used; the voltage range was 3.0-4.5V (NCM811, lithium-rich manganese-based) / 3.0-4.6V (LiCoO2), the charge-discharge rate was 0.5C (charging: constant current and constant voltage, cutoff current 0.05C; discharging: constant current); 200 cycles were performed, and the charge-discharge capacity and coulombic efficiency of each cycle were recorded.

[0063] 2. Interface Impedance (EIS) Test:

[0064] The CHI660E electrochemical workstation was used, with a frequency range of 10. -2 -10 5 Hz, AC amplitude 5mV, tested under open circuit voltage; test nodes are after the battery is at rest (initial state), after 100 cycles and after 200 cycles. The equivalent circuit is fitted by ZsimpWin software and the charge transfer impedance (Rct) is extracted.

[0065] 3. Ratio Performance Test:

[0066] The LAND CT2001A charge-discharge tester was used. The voltage range was the same as the cyclic test. The charge-discharge rates were 0.2C, 0.5C, 1C, 2C and 5C respectively. Each rate was cycled 5 times and the discharge capacity at each rate was recorded.

[0067] Please refer to Table 1 below. The cycling stability was significantly improved. After 200 cycles, the capacity retention rates of the experimental group samples reached 82.4%, 76.3%, and 72.1%, respectively, which were all higher than those of the corresponding control group samples (CK1, CK2, and CK3), indicating that the composite coating layer effectively suppressed capacity decay. The average coulombic efficiency of the modified samples was higher than 99.1%, which was significantly better than that of the unmodified samples (98.2%-98.8%), indicating that the interfacial side reactions were greatly suppressed and the loss of active substances was reduced.

[0068] Table 1 Cyclic stability data

[0069] Sample number Initial discharge capacity (mAh / g) Discharge capacity after 100 cycles (mAh / g) Capacity retention rate after 100 cycles (%) 200-cycle discharge capacity (mAh / g) Capacity retention rate after 200 cycles (%) Average coulomb efficiency (1-200 times, %) CK1 195.2 136.8 69.9 112.4 57.6 98.8 CK2 168.5 110.2 65.4 88.7 52.6 98.5 CK3 225.6 148.3 65.7 112.8 50.0 98.2 Experimental group 1 192.5 171.3 89.0 158.7 82.4 99.6 Experimental group 2 165.8 142.3 85.8 126.5 76.3 99.4 Experimental group 3 220.4 185.7 84.3 158.9 72.1 99.1

[0070] Please refer to Table 2 below. The increase in interfacial impedance was effectively suppressed. After 200 cycles, the Rct of the control group sample increased by 4.85-5.15 times, while that of the experimental group sample increased by only 1.96-2.23 times. This reflects the synergistic effect of the composite coating layer (metal oxide and amorphous carbon): the amorphous carbon network reduces electron transport resistance, the metal oxide blocks electrolyte erosion, and reduces the surge in interfacial impedance.

[0071] Table 2 Interface Impedance (Rct) Data

[0072] Sample number <![CDATA[Initial Rct (Ω·cm 2 )]]> <![CDATA[Rct (Ω·cm) after 100 cycles 2 > <![CDATA[Rct (Ω·cm) after 200 cycles 2 )]]> Rct growth factor (200 times / initial) CK1 85.6 242.8 415.3 4.85 CK2 78.9 215.4 382.7 4.85 CK3 102.5 286.3 528.4 5.15 Experimental group 1 92.3 145.7 188.6 2.04 Experimental group 2 86.5 132.6 169.8 1.96 Experimental group 3 108.7 175.2 242.3 2.23

[0073] Please refer to Table 3 below. With optimized rate performance, the 5C / 0.2C capacity ratio of the experimental group samples reached 78.1%-82.0%, which is 12-16 percentage points higher than that of the control group samples (65.4%-68.8%). This indicates that the high conductivity (carbon phase) of the composite coating layer and the ion transport channels (metal oxide phase) synergistically improve the charge transfer efficiency, meeting the requirements of high-rate charge and discharge.

[0074] Table 3 Ratio Performance Data

[0075] Sample number 0.2C discharge capacity (mAh / g) 0.5C discharge capacity (mAh / g) 1C discharge capacity (mAh / g) 2C discharge capacity (mAh / g) 5C discharge capacity (mAh / g) 5C / 0.2C capacity ratio (%) CK1 201.5 195.2 182.6 165.8 138.7 68.8 CK2 175.3 168.5 156.8 142.3 115.6 65.9 CK3 232.8 225.6 208.5 186.4 152.3 65.4 Experimental group 1 198.3 192.5 185.4 178.2 162.5 82.0 Experimental group 2 172.1 165.8 159.6 152.4 138.7 80.6 Experimental group 3 228.6 220.4 212.8 201.5 178.6 78.1

[0076] The foregoing has only described certain exemplary embodiments of the present invention by way of illustration. Undoubtedly, those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the foregoing drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. A surface treatment method for improving the cycle stability of high-voltage cathode materials, characterized in that, Includes the following steps: S1. Place the high-voltage cathode material powder in a weakly acidic aqueous solution with a pH of 3-6 or an aqueous solution containing an aminocarboxylic acid complexing agent, and perform surface pretreatment at 50-70℃ for 1-2 hours. Then wash and dry to obtain the treated cathode material. S2. The treated cathode material is immersed in a homogeneous precursor mixture solution containing a metal source and a carbon source to obtain the immersed material. S3. The impregnated material is heated to 300-500℃ in an oxidizing atmosphere and kept at this temperature for 2-4 hours to form a composite coating layer on the surface of the high voltage cathode material particles, thereby obtaining the modified material. S4. Under an inert atmosphere, the modified material is heated to 600-750℃ and held for 1-2 hours to obtain a cycle-stable high-voltage cathode material.

2. The surface treatment method for improving the cycle stability of high-voltage cathode materials according to claim 1, characterized in that, The high-voltage cathode material mentioned in S1 is high-voltage lithium cobalt oxide, with the general chemical formula LiNi. x Co y Mn z O2-rich high-nickel ternary materials or lithium-rich manganese-based lattice materials with reversible anionic redox reactions.

3. The surface treatment method for improving the cycle stability of high-voltage cathode materials according to claim 2, characterized in that, The general chemical formula is LiNi x Co y Mn z O2 high-nickel ternary material, where x≥0.6 and x+y+z=1.

4. The surface treatment method for improving the cycle stability of high-voltage cathode materials according to claim 1, characterized in that, The weakly acidic aqueous solution described in S1 is a dilute acetic acid, dilute citric acid, or a carbon dioxide-saturated aqueous solution.

5. The surface treatment method for improving the cycle stability of high-voltage cathode materials according to claim 1, characterized in that, The metal source in S2 is an alkoxide or organic acid salt of aluminum, zirconium, or titanium, and the carbon source in S2 is sucrose, glucose, citric acid, or polyethylene glycol.

6. The surface treatment method for improving the cycle stability of high-voltage cathode materials according to claim 5, characterized in that, The alkoxide is aluminum isopropoxide, tetrabutyl titanate, or tetrabutyl zirconate; the organic acid salt is acetate or citrate.

7. The surface treatment method for improving the cycle stability of high-voltage cathode materials according to claim 1, characterized in that, The thickness of the composite coating layer described in S3 is 5-30 nm.

8. The surface treatment method for improving the cycle stability of high-voltage cathode materials according to claim 1, characterized in that, The heating rate described in S4 for heating to 600-750℃ is 3-10℃ / min.

9. The surface treatment method for improving the cycle stability of high-voltage cathode materials according to claim 1, characterized in that, The heating rate for raising the temperature to 300-500℃ as described in S3 is 2-5℃ / min.

10. A high-voltage cathode material, characterized in that, It is prepared by the surface treatment method for improving the cycle stability of high voltage cathode materials as described in any one of claims 1-9.

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