Lithium cobalt oxide cathode materials with surface coating, their preparation methods and applications

Abstract

This invention discloses a lithium cobalt oxide cathode material with a surface coating, its preparation method, and its application, comprising the following steps: Step S1: Weighing a substance and dissolving it in a solvent, then ultrasonically treating the solution; Step S2: Weighing the lithium cobalt oxide cathode material and adding it to the solvent of Step S1, heating and stirring until evaporated to dryness, and then drying it in a constant temperature oven; Step S3: Mechanically fusing and coating the powder obtained in Step S2, followed by calcination to obtain the modified lithium cobalt oxide cathode material. The invention forms a stable, thick surface structure on the surface of the modified lithium cobalt oxide particles, effectively suppressing the stress and strain of the lithium cobalt oxide cathode material during cycling. After 100 cycles, the original lithium cobalt oxide particles break down, while the modified lithium cobalt oxide particles maintain an intact structure, indicating that this modification method can eliminate localized stress unevenness and continuous reactions during cycling, thereby obtaining excellent long-cycle performance and rate performance.

Description

Technical Field

[0001] This invention relates to a lithium cobalt oxide cathode material with a surface coating, and more particularly to a lithium cobalt oxide cathode material coated with an electron-ion hybrid conductor that operates stably under high voltage, its preparation method and application, belonging to the field of lithium-ion battery cathode materials. Background Technology

[0002] Lithium-ion batteries, due to their high energy density and long cycle life, have become the mainstream energy storage technology in portable electronics, new energy vehicles, and grid energy storage. Lithium cobalt oxide (LiCoO2, LCO) is particularly noteworthy due to its high theoretical capacity (274 mAh g⁻¹). -1 High operating voltage (typically 4.2 V) and high density (5.05 g / cm³) -3 Lithium-ion batteries are widely used in consumer electronics. With industry development, the demand for high energy density and long cycle life lithium-ion batteries continues to increase. To achieve higher energy density, the charge / discharge cutoff voltage needs to be increased to 4.5 V or even higher, but this also leads to irreversible structural transformations at high voltages, lattice oxygen loss, and undesirable interfacial side reactions with the electrolyte, resulting in rapid capacity decay and reduced cycle stability.

[0003] In recent years, various strategies have been proposed for stabilizing high-voltage LCOs, including modification methods such as trace element doping and surface coating. Element doping enhances stability and conductivity by adjusting the crystal and electronic structures. Surface coating involves applying a protective layer to the surface to isolate the electrolyte and buffer phase transition stress. Researchers have developed a variety of coating materials, including metal oxides, fluorides, lithium-ion conductors, and electronic conductors, to suppress interfacial side reactions and enhance structural stability. Both element doping and surface coating can significantly improve the structural stability and cycling performance of LCOs.

[0004] CN104201323B discloses a method for preparing an alumina-coated lithium cobalt oxide cathode material, which involves uniformly coating an alumina film onto the surface of lithium cobalt oxide using a vapor deposition method. The alumina-coated modified lithium cobalt oxide cathode material synthesized by this method exhibits uniform alumina coating and excellent cycle stability. However, the use of only an inert oxide coating layer can inhibit the rapid transport of lithium ions.

[0005] CN114335534A discloses a lithium cobalt oxide cathode material modified with lithium zirconium phosphate fast ion conductor coating. The lithium zirconium phosphate fast ion conductor is coated on the surface of the lithium cobalt oxide cathode material and forms microparticles, exhibiting excellent rate performance and cycle stability at a higher charging voltage of 4.6 V. However, the cycle capacity retention is low, and there is no electronic conductor.

[0006] In summary, while inert coatings can suppress interfacial side reactions and enhance surface stability compared to existing technologies, they also hinder Li⁺ conduction. Ionic conductors, on the other hand, offer high ionic conductivity and isolate electrolyte side reactions, but lack sufficient electronic conductivity. This invention utilizes a mixed coating of electronic and ionic conductors to form a stable, thick coating interface, which promotes lithium-ion transport and electronic conduction, suppresses the increase in interfacial impedance, improves kinetic performance, and exhibits superior electrochemical performance. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides a lithium cobalt oxide cathode material with a surface coating layer, its preparation method, and its application. By coating lithium cobalt oxide (LiCoO2) with an electron-ion mixed conductor, a robust physical and chemical barrier can be formed, stabilizing the interface and preventing the dissolution of transition metals, thereby improving kinetic and electrochemical performance.

[0008] To solve the above technical problems, the technical solution adopted by the present invention is: a method for preparing lithium cobalt oxide cathode material with a surface coating layer, comprising the following steps: Step S1: Weigh an appropriate amount of ionic conductor and electronic conductor, dissolve the above substances in a solvent, and sonicate the solution under certain conditions; Step S2: Weigh an appropriate amount of lithium cobalt oxide cathode material and add it to the solvent obtained in step S1. Heat and stir under certain conditions until it becomes powder, and then dry it in a constant temperature oven. Step S3: The powder obtained in step S2 is mechanically fused and coated and then calcined to obtain a modified lithium cobalt oxide cathode material.

[0009] Preferably, in step S1, the ionic conductor is selected from any one of nano lithium phosphate, lithium titanium aluminum phosphate, and lithium niobate, and the electronic conductor is selected from any one of conductive carbon black, aluminum-doped zinc oxide, and tin-doped indium oxide.

[0010] Preferably, in step S1, the ion conductor is 1-3 wt% of the weight of the LCO used, the electron conductor is 20-50 wt% of the weight of the ion conductor used, the solvent is anhydrous ethanol or ultrapure water, and the ultrasonic conditions are ultrasonic power of 80% of the maximum allowable amplitude of the equipment for 1 hour.

[0011] Preferably, in step S2, the amount of lithium cobalt oxide cathode material added is 100-300 g.

[0012] Preferably, in step S2, the heating and stirring are carried out on a constant temperature magnetic stirrer, with a heating temperature of 60-100°C, a stirring speed of 400-800 rpm, and a stirring time of 8-12 h; the drying conditions are drying in a constant temperature oven at 80°C for 8-12 h.

[0013] Preferably, in step S3, the mechanical fusion coating is performed in a mechanical fusion machine at a speed of 3000-5000 rpm for a duration of 10-30 min.

[0014] Preferably, in step S3, the calcination temperature is 200-1000°C and the calcination time is 1-6 h.

[0015] The lithium cobalt oxide cathode material with a surface coating layer prepared by the preparation method includes an outer surface coating layer and an inner bulk phase. The surface coating layer is composed of uniformly distributed electron-ion conductors, and the bulk phase is unmodified layered lithium cobalt oxide.

[0016] Preferably, the lithium cobalt oxide matrix is ​​composed of smooth-surfaced microparticles with a particle size of 2-15 μm, and the thickness of the surface coating layer is 10-15 nm.

[0017] The application of surface-coated lithium cobalt oxide cathode material is to use lithium cobalt oxide cathode material as the cathode material of lithium-ion batteries.

[0018] This invention uses a mechanical fusion method to feed the mixed powder into a narrow processing cavity. The rotor inside the cavity moves at high speed, applying strong mechanical forces such as compression, shearing and friction to the material, which allows the nanoscale coating material to coat a uniform and dense coating layer on the surface of lithium cobalt oxide, thus constructing a stable interface.

[0019] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention uses nanoscale lithium titanium aluminum phosphate and aluminum-doped zinc oxide as coating materials, expanding the application of lithium titanium aluminum phosphate from the field of all-solid-state batteries to the field of liquid batteries.

[0020] 2. This invention uses a mixed surface coating of lithium titanium aluminum phosphate and aluminum-doped zinc oxide as an artificial CEI layer, constructing a 10-15 nm coating layer on the surface. Electrochemical impedance spectroscopy (EIS) tests were performed on the original lithium cobalt oxide and modified lithium cobalt oxide before cycling, and after the first, 20, 50, and 100 cycles following activation. The results show that, with cycling, the internal resistance R of the original and modified lithium cobalt oxide decreases. s and surface film resistance R sf They are basically the same, but the original charge transfer resistance R ct As the loop continues, R ct The Ω gradually increased from 64.03 Ω before cycling to 524.2 Ω after 100 cycles, while the modified lithium cobalt oxide R ct The Ω value stabilized at 218.7 Ω after 100 cycles, up from 84.82 Ω before cycling. The modification method effectively enhanced the interfacial chemical stability and improved the electrochemical performance of the lithium cobalt oxide cathode material under high voltage.

[0021] 3. The lithium cobalt oxide cathode material prepared by this invention has a coating material consisting of electronic and ion-conducting particles, which facilitates ion transport and electron conduction, and possesses rapid Li-ionization properties. + Excellent rate performance is achieved through transmission dynamics and a small increase in cyclic impedance.

[0022] 4. The lithium cobalt oxide cathode material co-coated with an electron-ion hybrid conductor prepared in this invention can be used to assemble conventional coin cells at 3-4.6 V and 137 mA g. -1 It still has 187.5 mAh g after 100 cycles. -1 It has a discharge specific capacity and a capacity retention rate of 90.5%.

[0023] This invention forms a stable, thick surface structure on the lithium cobalt oxide surface, expanding the application scenarios of lithium titanium aluminum phosphate. It effectively suppresses the increase in impedance and stress strain of the lithium cobalt oxide cathode material during cycling. After 100 cycles, the original lithium cobalt oxide particles break down, while the modified lithium cobalt oxide particles still maintain an intact structure. This indicates that the modification method can eliminate local stress unevenness and continuous reaction during cycling, and provides a structural basis for rapid lithium ion insertion and extraction, thereby achieving excellent long-cycle performance and rate performance.

[0024] This invention forms a uniform and stable thick coating interface, preventing the dissolution of transition metals. EDS linear scanning of the original lithium cobalt oxide and modified lithium cobalt oxide battery separators after 100 cycles revealed characteristic peaks of Co on the original lithium cobalt oxide separator, while no characteristic peaks of Co were detected in the vicinity of the modified lithium cobalt oxide sample. This indicates that constructing a uniform thick coating layer weakens the oxidation and precipitation of Co and plays a crucial role in improving the reversibility of Co participation in the reaction.

[0025] The synthesis process of this invention is simple, employing conventional solid-phase reaction and mechanical fusion methods, resulting in low cost, large and stable yield, and facilitating large-scale industrial production. This invention enables the full application of lithium titanium aluminum phosphate in high-energy-density batteries, providing a feasible approach for the commercialization of lithium titanium aluminum phosphate in lithium-ion batteries. Attached Figure Description

[0026] Figure 1 These are scanning electron microscope images of the cathode materials in Embodiment 1 and Comparative Example 1 of the present invention; Figure 2 This is a transmission electron microscope image of the modified lithium cobalt oxide cathode material of Example 1 of the present invention; Figure 3 These are the X-ray diffraction patterns of the cathode materials in Embodiment 1 and Comparative Example 1 of the present invention; Figure 4 These are cycle performance diagrams of the batteries assembled with the cathode materials in Embodiment 1 and Comparative Example 1 of the present invention; Figure 5 These are the fitting curves and R values ​​of the electrochemical impedance spectroscopy (EIS) tests of the cathode materials in Embodiment 1 and Comparative Example 1 before cycling, and after the first, 20, 50, and 100 cycles following activation. ct Comparison chart; Figure 6 These are the constant current intermittent titration curves and lithium ion diffusion coefficient diagrams of the positive electrode materials in the initial state and after 100 cycles in Example 1 and Comparative Example 1 of this invention. Figure 7 Electron conductivity diagrams of the cathode materials under different load pressures in Embodiment 1 and Comparative Example 1 of this invention; Figure 8 These are SEM images of the electrode particle morphology after 100 cycles of the positive electrode material in Embodiment 1 and Comparative Example 1 of the present invention. Figure 9 This is an EDS linear scan of the separator of the positive electrode material in Embodiment 1 and Comparative Example 1 of the present invention after 100 cycles. Detailed Implementation

[0027] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0028] In the following embodiments, the lithium cobalt oxide cathode material is selected from commercial lithium cobalt oxide from Tianjin Guoan Mengguli New Material Technology Co., Ltd.

[0029] Example 1 A method for preparing lithium cobalt oxide cathode material with a surface coating includes the following steps: 1. Weigh 6 g of nano-lithium titanium aluminum phosphate and 1.2 g of nano-aluminum doped zinc oxide, mix them with an appropriate amount of anhydrous ethanol in a beaker, and sonicate them in an ultrasonic machine at 80% power for 1 h until a uniformly dispersed mixed solution of nano-lithium titanium aluminum phosphate and nano-aluminum doped zinc oxide is obtained.

[0030] 2. Weigh 300 g of raw LCO and add it to the mixed solution from step 1 above. Continue to add anhydrous ethanol to the 500 mL mark in the beaker, and place it on a thermostatic magnetic stirrer to continue heating and stirring. Set the stirring temperature and stirring speed to 80°C and 400 rpm, respectively, for 12 h. Place the obtained evaporated material and the beaker in an 80°C thermostatic oven for further drying for 12 h.

[0031] 3. Add the completely dry powder obtained in step 2 above to a mechanical fusion machine for mechanical fusion coating. The coating conditions are set as follows: rotation speed 4000 rpm and time 20 min, to obtain LCO cathode material with uniform coating of nano-lithium titanium aluminum phosphate and aluminum-doped zinc oxide.

[0032] 4. The uniformly coated LCO material was calcined in a muffle furnace at 200°C for 4 hours in air atmosphere (heating rate of 5°C / min). -1 The final product consists of a thick outermost coating layer, uniformly distributed with electron-ion conductor nano-lithium titanium aluminum phosphate and aluminum-doped zinc oxide, while the bulk phase remains unmodified layered lithium cobalt oxide. Its electrochemical performance is shown in Table 1.

[0033] Example 2 The difference between this embodiment and Example 1 is that nano-lithium aluminum titanium phosphate is not added in step 1, while the other steps are the same as in Example 1. Its electrochemical performance is shown in Table 1.

[0034] Example 3 The difference between this embodiment and Example 1 is that no nano-aluminum-doped zinc oxide is added in step 1, while the other steps are the same as in Example 1. Its electrochemical performance is shown in Table 1.

[0035] Example 4 The difference between this embodiment and Example 1 is that: in step 1, half the content of nano-lithium aluminum titanium phosphate from Example 1 is added, while the other steps are the same as in Example 1. Its electrochemical performance is shown in Table 1.

[0036] Example 5 The difference between this embodiment and Example 1 is that the aluminum-doped zinc oxide content of Example 1 is twice that of Example 1 in step 1, while the other steps are the same as in Example 1. Its electrochemical performance is shown in Table 1.

[0037] Example 6 The difference between this embodiment and Example 1 is that the calcination step in Example 1 is removed, while the other steps are the same as in Example 1. Its electrochemical performance is shown in Table 1.

[0038] Example 7 The difference between this embodiment and Example 1 is that the calcination step in Example 1 is changed to calcination at 350°C in an air atmosphere. The other steps are the same as in Example 1. Its electrochemical performance is shown in Table 1.

[0039] Example 8 The difference between this embodiment and Example 1 is that the calcination step in Example 1 is changed to calcination at 500°C in an air atmosphere. The other steps are the same as in Example 1. Its electrochemical performance is shown in Table 1.

[0040] Example 9 The difference between this embodiment and Example 1 is that the calcination and heat preservation time in Example 1 is changed to 2 h, while the other steps are the same as in Example 1. Its electrochemical performance is shown in Table 1.

[0041] Example 10 The difference between this embodiment and Example 1 is that the calcination and heat preservation time in Example 1 is changed to 6 h, while the other steps are the same as in Example 1. Its electrochemical performance is shown in Table 1.

[0042] Example 11 The difference between this embodiment and Example 1 is that the nano-aluminum doped zinc oxide in step 1 is replaced with conductive carbon black Super P Li, and the sintering in air is replaced with sintering under an inert gas atmosphere. The other steps are the same as in Example 1, and its electrochemical performance is shown in Table 1.

[0043] Example 12 The difference between this embodiment and Embodiment 1 is that the nano-aluminum doped zinc oxide in step 1 is replaced with Ketjen Black KEC600JD, and the sintering in air is replaced with sintering under inert gas protection. The other steps are the same as in Embodiment 1. Its electrochemical performance is shown in Table 1.

[0044] Example 13 The difference between this embodiment and Embodiment 1 is that the nano-aluminum doped zinc oxide in step 1 is replaced with carbon nanotubes (CNTs), and the sintering in air is replaced with sintering under inert gas protection. The other steps are the same as in Embodiment 1. Its electrochemical performance is shown in Table 1.

[0045] Comparative Example 1 The comparative example only used raw lithium cobalt oxide for cycle performance testing, and its electrochemical performance is shown in Table 1.

[0046] The structural and morphological characteristics of the cathode material before and after treatment were analyzed, and the results are as follows: Scanning electron microscopy (SEM) images of Example 1 and Comparative Example 1 are as follows: Figure 1 As shown. In this example, the modified lithium cobalt oxide from Example 1 is denoted as LA-LCO. Figure 1 The image on the left is a SEM image of Comparative Example 1. The LCO particles selected in the image have a particle size of 2-5 μm and a smooth surface. The broken LCO particles did not affect their surface morphology. Figure 1 The image on the right is an SEM image of Example 1. As can be seen from the image, the particle size of the modified LCO particles is 2-5 µm, the surface is relatively smooth, and the coating effect is good.

[0047] High-resolution transmission electron microscopy (HR-TEM) image of the sample in Example 1 is shown below. Figure 2 As shown, Figure 2 Image a is a TEM image of the LCO particles coated with an electron-ion mixed conductor in Example 1, showing different contrasts inside and outside the particles. Figure 2 b is Figure 2A magnified view of region 1 in image a shows a uniform coating layer approximately 10 nm thick on the particle surface. Analysis reveals that nano-lithium aluminum titanium phosphate and aluminum-doped zinc oxide are interspersed on the surface, with a spinel-like transition layer at the subsurface and a layered lithium cobalt oxide matrix near the surface.

[0048] Figure 3 Comparing the XRD images of the samples from Example 1 and Comparative Example 1, the images show that the diffraction peaks before and after modification largely coincide with the standard PDF card of LCO X-ray diffraction, indicating that the α-NaFeO2 layered structure of the R-3m space group is maintained before and after modification. The peak position of (003) peak remains basically unchanged, indicating that the modification treatment has little effect on the c-axis change of LCO.

[0049] The specific steps for preparing the positive electrode and assembling the coin cells in the above embodiments and comparative examples are as follows: Positive electrode preparation: First, raw lithium cobalt oxide powder, polyvinylidene fluoride (PVDF), and acetylene black were mixed in a ratio of 8:1:1, and then an appropriate amount of N-methyl-2-pyrrolidone was added and stirred using a degassing mixer. Next, the obtained slurry mixture was coated onto aluminum foil and dried in a constant temperature oven at 70°C for 3 hours to form a circular electrode with a diameter of 10 mm. Finally, it was dried at 100°C under negative pressure for 12 hours to obtain the desired positive electrode.

[0050] Button cell assembly: In a glove box under a high-purity argon atmosphere, a polyethylene membrane with a single-sided Al2O3 coating is used as the separator, 8335 (1M LiPF6 dissolved in a 1:1 volume ratio of ethylene carbonate (EC) and dimethyl carbonate (EMC) solvent) is used as the electrolyte, and a lithium sheet is used as the counter electrode. Together with the above-mentioned positive electrode sheet, the button cell (CR2032) is assembled from bottom to top in the following order: negative electrode shell, spring, gasket, negative electrode (lithium sheet), electrolyte (60 μL), separator, positive electrode, and positive electrode shell.

[0051] Electrochemical performance test results and analysis: Electrochemical performance tests were conducted on Examples 1-13 and Comparative Example 1 at room temperature. All tests were performed using coin cells at voltages of 3.0-4.6 V and 137 mA g. -1 The current density (27.4 mA g for the first three weeks) -1 The results were obtained from the following tests. Table 1 lists the electrochemical performance test results of Examples 1-13 and Comparative Example 1, as shown in the table below: Table 1. Electrochemical performance test results of the examples and comparative examples.

[0052] By comparing the electrochemical performance data in the table above, the following conclusions can be drawn: (1) Comparing the electrochemical performance of Examples 1-13 and Comparative Example 1, Table 1 shows that, compared with the unmodified form, the modified lithium cobalt oxide cathode material exhibits varying degrees of optimization during long-term cycling. In most examples, the discharge specific capacity in the first cycle did not increase compared to the comparative example, which is due to the increased interfacial barrier caused by the coating. However, the coulombic efficiency in the first cycle was higher than that of the original LCO, indicating that the coating layer isolated the electrolyte from the contact between electrons and the cathode. Furthermore, the discharge specific capacity after 100 cycles was significantly higher than that of the original LCO, indicating that the coating layer blocked the escape of lattice oxygen, preventing stress cracking and continuous increase in interfacial impedance, thus improving cycle performance. This demonstrates that the treatment scheme plays an important role in improving the performance of the cathode material.

[0053] (2) The test results of Comparative Example 1 and Comparative Example 1 are as follows: Figure 4 As shown in the figure. Clearly, the initial discharge specific capacity of the modified samples is significantly greater than that of the original LCO, and the first-cycle coulombic efficiency is also higher than that of LCO. After 100 cycles, the capacity retention of the modified lithium cobalt oxide cathode material is much higher than that of the original lithium cobalt oxide, with a discharge specific capacity still reaching 187.5 mAh g⁻¹. -1 The capacity decay is much lower than that of the original lithium cobalt oxide cathode material (76.5 mAh g). -1 The results indicate that the modified cathode exhibits superior cycle performance compared to the original lithium cobalt oxide. This is primarily due to the formation of a relatively uniform and dense surface coating layer under the co-coating of nano-lithium aluminum titanium phosphate (LATP) and AZO, which effectively suppresses interfacial side reactions and irreversible phase transitions, thus contributing to the cycle stability of the lithium cobalt oxide structure.

[0054] (3) Comparing Examples 1-3, under the same experimental conditions, the effect of coating with a single material on electrochemical performance was observed. The first-week discharge specific capacity of the sample coated with only LATP (Example 2) and the sample coated with only AZO (Example 3) were 205.1 mAh g, respectively. -1 and 199.2 mAh g -1 The first-cycle coulombic efficiency was similar to that of the mixed-coated sample (Example 1), but the discharge specific capacity after 100 cycles in Example 2 was 140.6 mAh g⁻¹. -1 Example 3 is 146.7 mAh g -1 This is significantly lower than the 187.5 mAh g of the mixed-coating Example 1. -1 The capacity retention rate was also lower than that of Example 1, indicating that the mixed coating can improve cycle performance.

[0055] (4) Comparing Examples 1 and 4-5, under the same experimental conditions, the effect of different coating contents on electrochemical performance was observed. In Example 4, the mass of LATP was 50% of that in Example 1, and the discharge specific capacity after 100 cycles was 163.0 mAh g.-1 In Example 4, the mass of AZO was 200% of that in Example 1, and the discharge specific capacity after 100 cycles was 169.3 mAh g. -1 By reducing or increasing the amount of coating, it was found that the cycling performance decreased after 100 cycles, indicating that the coating amount helps to obtain the best electrochemical performance.

[0056] (5) Comparing Examples 1 and 6-8, under the same experimental conditions, the effect of different calcination temperatures on electrochemical performance was observed. As shown in Table 1, the first-cycle discharge specific capacity of Example 6 (without sintering treatment) and Example 7 (sintering temperature 350°C) was 195.9 mAh g⁻¹. -1 and 197.1 mAh g -1 Furthermore, the discharge specific capacity after 100 cycles is significantly higher than 168.1 mAh g. -1 and 162.4 mAh g -1 The specific capacity of Example 8 was significantly lower than that of Example 1, even though the discharge specific capacity after 100 cycles was similar to that of Example 1. This indicates that the battery exhibits optimal electrochemical performance at a calcination temperature of 200°C. This suggests that this temperature is conducive to the formation of a stable interface, promoting lithium-ion transport and thus achieving optimal electrochemical performance.

[0057] (6) Comparing Examples 1 and 9-10, under the same experimental conditions, the effect of different heat preservation times on electrochemical performance was observed. As shown in Table 1, the discharge specific capacity in the first week was 193.2 mAh g when the heat preservation time was 2 h and 6 h, respectively. -1 and 200.7 mAh g -1 Furthermore, the discharge specific capacity after 100 cycles was 163.3 mAh g. -1 and 157.1mAh g -1 The values ​​were all significantly lower than in Example 1. This indicates that the battery exhibited optimal electrochemical performance only after being kept at this temperature for 4 hours. This demonstrates that the duration of the heat treatment also affects the structure, and this temperature is beneficial for obtaining optimal electrochemical performance.

[0058] (7) Comparing Examples 1 and 11-13, under the same experimental conditions, the effect of using different electronic conductors on electrochemical performance was observed. As shown in Table 1, using conductive carbon blacks of different morphologies, Super P Li, Ketjen Black KEC 600JD, and carbon nanotubes (CNTs), the first-cycle discharge specific capacity was 179.1 mAh g⁻¹, respectively. -1 188.9 mAh g -1 and 184.5 mAh g -1This significantly reduced the discharge specific capacity in the first cycle. After 100 cycles, the discharge specific capacity was 132.3 mAh g. -1 151.4 mAh g -1 and 143.4 mAh g -1 The results are significantly lower than those using aluminum-doped zinc oxide, indicating that this electronic conductor coating can significantly improve cycle performance.

[0059] In summary, by exploring the coating of individual electronic or ionic conductors under different experimental conditions, different coating contents, different sintering temperatures, different holding times, and different electronic conductor coatings, it was found that using a mixture of lithium titanium aluminum phosphate and aluminum-doped zinc oxide to coat lithium cobalt oxide, with contents of 6 g and 1.2 g respectively, at a sintering temperature of 200°C and a holding time of 4 h, can obtain a stable, uniform, and thick coating layer, which promotes the suppression of interfacial side reactions, promotes lithium-ion transport and electron conduction, and improves electrochemical and kinetic performance.

[0060] Furthermore, by comparing the positive electrode material batteries in Example 1 and Comparative Example 1 before cycling ( Figure 5 a) First time after activation ( Figure 5 b) 20 times ( Figure 5 c) 50 times ( Figure 5 d) and 100 times ( Figure 5 e) The corresponding fitted curve of the electrochemical impedance spectroscopy after cycling, and the charge transfer resistance R ct Comparison and fitted values ​​(Table 2). Internal resistance R of modified lithium cobalt oxide before cycling. s and charge transfer resistance R ct The higher resistance (R) compared to LCO is due to surface coating. As cycling progresses, the internal resistance R of both the original lithium cobalt oxide and the modified lithium cobalt oxide decreases. s and surface film resistance R sf Basically the same, R sf Gradually decrease; while LCO's R ct The Ω gradually increased from 64.03 Ω before cycling to 524.2 Ω after 100 cycles, while the modified lithium cobalt oxide R ct The charge transfer resistance R of the modified sample increased from 84.82 Ω before cycling to 235.7 Ω in the first week after activation, then remained stable, and decreased to 218.7 Ω after 100 cycles. ct The smaller and more stable enhancement of interfacial chemical stability improves the electrochemical performance of lithium cobalt oxide cathode materials under high voltage.

[0061] Table 2 shows the EIS fitting values ​​of the cathode materials in Example 1 and Comparative Example 1 of the present invention before cycling, and after the first, 20th, 50th, and 100th cycles after activation. By comparing the cathode materials in Example 1 and Comparative Example 1 in their initial state ( Figure 6 a) and 100 times ( Figure 6 b) After cycling, the sample was subjected to constant current intermittent titration and the lithium-ion diffusion coefficient was calculated. Figure 6 During the first cycle, the charge-discharge curves of the original lithium cobalt oxide and the modified LA-LCO sample were roughly the same. Figure 6 a), but after 100 cycles, the GITT curve of the original lithium cobalt oxide changed significantly, while the GITT curve of the modified LA-LCO sample remained basically unchanged. Figure 6 (b) This difference in curves also demonstrates that the modified LA-LCO sample has a more repeatable voltage response. Although the lithium-ion diffusion coefficient of the modified LA-LCO before cycling is not significantly different from that of LCO ( Figure 6 c), however, the lithium-ion diffusion coefficient of the modified LA-LCO after cycling is always higher than that of the original LCO, and compared with the charging process, the lithium-ion diffusion coefficient of LCO continues to decay during the discharge process, while that of LA-LCO remains consistent with that during the charging process. Figure 6 d). This is because LATP provides Li + The transmission channel is Li + The embedding of the material creates a more robust kinetic structure, which results in a superior lithium-ion diffusion coefficient during discharge compared to the charging process, indicating that the modification treatment significantly optimizes the kinetic performance of LCO.

[0062] The electronic conductivity of the cathode materials in Example 1 and Comparative Example 1 was tested under different load pressures, such as... Figure 7 As shown, the electronic conductivity of the sample increased linearly with increasing pressure, and the conductivity of the modified sample was consistently higher than that of the original lithium cobalt oxide. At a load pressure of 20 kN, the electronic conductivity of the original lithium cobalt oxide was 4.0 × 10⁻⁶ kN. -5 S cm -1 The modified lithium cobalt oxide sample had a strength of 1.5 × 10⁻⁶. -4 S cm -1 The higher electronic conductivity than LCO indicates that AZO coating of LCO is beneficial for promoting electronic conductivity and improving electrochemical performance.

[0063] The morphology of the electrode particles in the positive electrode materials of Example 1 and Comparative Example 1 after 100 cycles was observed by SEM. Figure 8 As shown, it was found that the original LCO particles broke down after 100 cycles. Figure 8 a), while the modified lithium cobalt oxide particles did not break down after 100 cycles ( Figure 8 (b) The modified LA-LCO particles still maintain good morphology after 100 cycles.

[0064] EDS linear scanning of the separators after 100 cycles of the cathode material batteries in Example 1 and Comparative Example 1 revealed that, Figure 9 As shown, obvious O, F, and P elemental signals are present on the membrane. The original lithium cobalt oxide membrane exhibits a characteristic peak for Co, while no Co characteristic peak was detected in the vicinity of the modified lithium cobalt oxide sample membrane. This indicates that constructing a uniform, thick coating layer weakens Co oxidation and precipitation, playing a crucial role in improving the reversibility of Co participation in the reaction.

[0065] The above embodiments are not intended to limit the present invention, and the present invention is not limited to the examples given above. Any changes, modifications, additions or substitutions made by those skilled in the art within the scope of the technical solution of the present invention are also within the protection scope of the present invention.

Claims

1. A method for preparing a lithium cobalt oxide cathode material with a surface coating, characterized in that: Includes the following steps: Step S1: Weigh an appropriate amount of ionic conductor and electronic conductor, dissolve the above substances in a solvent, and sonicate the solution under certain conditions; Step S2: Weigh an appropriate amount of lithium cobalt oxide cathode material and add it to the solvent obtained in step S1. Heat and stir under certain conditions until it evaporates to dryness, and then place it in a constant temperature oven to dry. Step S3: The powder obtained in step S2 is mechanically fused and coated and then calcined to obtain a modified lithium cobalt oxide cathode material.

2. The method for preparing the lithium cobalt oxide cathode material with a surface coating layer according to claim 1, characterized in that: In step S1, the ionic conductor is selected from any one of nano lithium phosphate, lithium titanium aluminum phosphate, and lithium niobate, and the electronic conductor is selected from any one of conductive carbon black, aluminum-doped zinc oxide, and tin-doped indium oxide.

3. The method for preparing the lithium cobalt oxide cathode material with a surface coating layer according to claim 2, characterized in that: In step S1, the ion conductor is 1-3 wt% of the weight of the LCO used, the electron conductor is 20-50 wt% of the weight of the ion conductor used, and the solvent is anhydrous ethanol or ultrapure water; the ultrasonic conditions are ultrasonic power of 80% of the maximum allowable amplitude of the equipment for 1 hour.

4. The method for preparing the lithium cobalt oxide cathode material with a surface coating layer according to claim 1, characterized in that: In step S2, the amount of lithium cobalt oxide cathode material added is 100-300 g.

5. The method for preparing the lithium cobalt oxide cathode material with a surface coating layer according to claim 1, characterized in that: In step S2, heating and stirring are carried out on a constant temperature magnetic stirrer at a heating temperature of 60-100°C, a stirring speed of 400-800 rpm, and a stirring time of 8-12 h; drying is carried out in a constant temperature oven at 80°C for 8-12 h.

6. The preparation method of the lithium cobalt oxide cathode material with a surface coating layer according to claim 1, characterized in that: In step S3, the mechanical fusion coating is performed in a mechanical fusion machine at a speed of 3000-5000 rpm for a duration of 10-30 min.

7. The preparation method of the lithium cobalt oxide cathode material with a surface coating layer according to claim 1, characterized in that: In step S3, the calcination temperature is 200-1000°C and the calcination time is 1-6 h.

8. A lithium cobalt oxide cathode material with a surface coating layer prepared by the preparation method according to any one of claims 1-7, characterized in that: The lithium cobalt oxide cathode material consists of an outer surface coating layer and an inner bulk phase. The surface coating layer is composed of uniformly distributed electron-ion conductors, and the bulk phase is unmodified layered lithium cobalt oxide.

9. The lithium cobalt oxide cathode material with a surface coating layer according to claim 8, characterized in that: The lithium cobalt oxide matrix is ​​composed of smooth-surfaced microparticles with a particle size of 2-15 μm, and the thickness of the surface coating layer is 10-15 nm.

10. The application of the surface-coated lithium cobalt oxide cathode material according to claim 9, characterized in that: Lithium cobalt oxide cathode material is used as the cathode material for lithium-ion batteries.

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