Modified lithium cobalt oxide cathode material, preparation method thereof and lithium ion battery

Abstract

This invention relates to the field of lithium-ion batteries, specifically disclosing a modified lithium cobalt oxide cathode material, its preparation method, and a lithium-ion battery. In this invention, the composite coating layer and the gradient transition layer work synergistically, both suppressing electrolyte erosion and harmful phase transitions through physical barriers, and broadening the Li-cobalt oxide layer through electrostatic repulsion between highly electronegative elements. + The transmission channel significantly improves the cycling stability, rate performance, and structural integrity of the material under high voltage. The preparation method provided by this invention is simple, controllable, energy-efficient, and easy to scale up. The resulting material exhibits excellent electrochemical performance in the 3.0–4.6 V voltage range, providing key material support for the application of high-voltage lithium-ion batteries.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion batteries, specifically to modified lithium cobalt oxide cathode materials, their preparation methods, and lithium-ion batteries. Background Technology

[0002] Lithium cobalt oxide, with its high volumetric energy density and excellent electrochemical kinetics performance, has become the mainstream cathode material for lithium-ion batteries in 3C electronic products. Its theoretical specific capacity is 185 mAh g⁻¹. -1 (vs.L) i+ However, in commercial applications, the charge / discharge cutoff voltage is limited to around 4.5 V. Increasing the cutoff voltage to 4.6 V would allow for the extraction of more Li. + The theoretical specific capacity is increased by 21%, reaching 220 mAh g. -1 This significantly improves battery energy density.

[0003] However, lithium cobalt oxide faces severe performance degradation under high voltage conditions of ≥4.55 V. During charging and discharging, deep intercalation and deintercalation of lithium ions lead to drastic changes in lattice parameters, causing interlayer slip and stress accumulation, disrupting lithium ion transport channels, and ultimately causing cracking of the cathode particles and rapid capacity decay. The underlying causes include, on the one hand, the large-scale extraction of Li+ ions from the surface leading to O2 degradation. 2- 2p and Co 3+ The deep overlap of 3d-t2g orbitals induces lattice oxygen to participate in redox reactions, producing high oxidation state Co. 4+ and O α- (α<2), which triggers harmful phase transitions and structural collapse on the surface; on the other hand, the HF generated by electrolyte decomposition will continue to erode the surface of lithium cobalt oxide, expose new active sites, exacerbate side reactions and structural damage, and ultimately lead to rapid capacity decay and shortened cycle life.

[0004] Existing improvement methods include electrolyte additive optimization, element doping, and surface coating. Among these, surface coating is an effective strategy for suppressing interfacial side reactions, and lithium niobate has a high Li+ conductivity (~10). -6 S cm -1 Lithium niobate nanoparticles, with their resistance to HF corrosion, are potential coating materials. However, as a highly polarizable ferroelectric crystal, lithium niobate nanoparticles tend to agglomerate at high temperatures and have weak interfacial bonding with lithium cobalt oxide, making them prone to detachment and difficult to form a uniform and stable coating layer. Furthermore, a single coating layer is insufficient to address the challenges posed by bulk Li. + Transport dynamics and structural stability issues. Elemental doping can broaden the transport dynamics of Li. + It provides a transmission channel, but it will deplete the active Li, resulting in a reduction in capacity.

[0005] Therefore, developing a composite coating system that combines excellent interfacial stability and ion transport characteristics with a simple and controllable preparation process to achieve a synergistic improvement in the structural stability and electrochemical performance of high-voltage LiCoO2 cathode materials has become a technical challenge that urgently needs to be solved in this field. Summary of the Invention

[0006] The purpose of this invention is to overcome the problems of poor structural stability and electrochemical performance of existing LiCoO2 cathode materials, and to provide a modified lithium cobalt oxide cathode material that combines structural stability and excellent electrochemical performance.

[0007] To achieve the above objectives, the present invention provides a modified lithium cobalt oxide cathode material, which comprises a lithium cobalt oxide matrix and a gradient transition layer and a composite coating layer sequentially coated on the outer surface of the lithium cobalt oxide matrix; The gradient transition layer consists of a spinel-like transition layer with gradient doping of magnesium, niobium, and fluorine elements from the inside out; the composite coating layer contains nano-sized lithium fluorinated niobate and nano-sized magnesium oxide.

[0008] A second aspect of the present invention provides a method for preparing a modified lithium cobalt oxide cathode material, the method comprising: S1: In the presence of a solvent, nano-lithium niobate, nano-magnesium oxide, fluorine source and lithium cobalt oxide are mixed and dried sequentially to prepare a composite precursor; S2: The composite precursor is calcined to prepare a modified lithium cobalt oxide cathode material.

[0009] A third aspect of the present invention provides a modified lithium cobalt oxide cathode material prepared by the method described in the second aspect of the present invention.

[0010] A fourth aspect of the present invention provides a lithium-ion battery in which the positive electrode comprises the modified lithium cobalt oxide positive electrode material described in the first aspect of the present invention.

[0011] The modified lithium cobalt oxide cathode material prepared by the above technical solution exhibits a synergistic effect between the composite coating layer and the gradient transition layer. This effect not only inhibits electrolyte erosion and harmful phase transitions through physical barriers but also broadens the Li-phase transition by utilizing the electrostatic repulsion between highly electronegative elements. + The transmission channel significantly improves the cycling stability, rate performance, and structural integrity of the material under high voltage. The preparation method provided by this invention is simple, controllable, energy-efficient, and easy to scale up. The resulting material exhibits excellent electrochemical performance in the 3.0-4.6 V voltage range, providing key material support for the application of high-voltage lithium-ion batteries. Attached Figure Description

[0012] Figure 1The images show a comparison of the transmission electron microscope (TEM) microstructures of the modified lithium cobalt oxide cathode materials prepared in Example 1, Comparative Example 1, and Comparative Example 2.

[0013] Figure 2 The image shows a selected region of the high-resolution transmission electron microscope (HR-TEM) image of the modified lithium cobalt oxide cathode material prepared in Example 1, represented by a fast Fourier transform (FFT) spectrum.

[0014] Figure 3 The X-ray diffraction (XRD) patterns of the samples from Example 1, Comparative Example 1, and Comparative Example 2 are shown below. Figure 4 These are the long-cycle capacity curves of the batteries in Example 1, Comparative Example 1, and Comparative Example 2 at 3.0-4.6 V and 0.5C. Figure 5 This is a comparison chart of the rate performance of the batteries in Example 1, Comparative Example 1, and Comparative Example 2 at 3.0-4.6 V; Figure 6 This is a comparison graph of the lithium-ion diffusion coefficients of the batteries in Example 1 and Comparative Example 1 before and after cycling. Detailed Implementation

[0015] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0016] The present invention provides a modified lithium cobalt oxide cathode material, the material comprising a lithium cobalt oxide matrix and a gradient transition layer and a composite coating layer sequentially coated on the outer surface of the lithium cobalt oxide matrix; The gradient transition layer consists of a spinel-like transition layer with gradient doping of magnesium, niobium, and fluorine elements from the inside out; the composite coating layer contains nano-sized lithium fluorinated niobate and nano-sized magnesium oxide.

[0017] In this invention, the gradient transition layer and the composite coating layer work synergistically to comprehensively improve the lithium cobalt oxide cathode material from two aspects: internal structural connectivity and external interface protection. The coating layer directly isolates electrolyte erosion, inhibits oxygen release, and accelerates lithium-ion interfacial transport. Meanwhile, the gradient transition layer, through gradient element doping and the pre-introduction of a spinel-like structure, effectively alleviates the internal stress caused by lattice mismatch and volume changes during charging and discharging, preventing particle cracking and harmful phase transitions from penetrating the bulk phase. It also improves the lattice matching degree between the composite coating layer and the substrate, inhibiting the shedding of the composite coating layer. The two layers work together to construct a stable, voltage-resistant structure with smooth lithium-ion transport, significantly improving the material's cycle stability, rate performance, and safety under high voltage.

[0018] The present invention introduces Nb and Mg elements to form high bond energy Nb-O and Mg-O, which can stabilize lattice oxygen and reduce oxygen precipitation and Co dissolution; the gradient doping structure suppresses the harmful phase transition O3→H1-3, which significantly reduces stress and strain accumulation during cycling, and the capacity retention rate is ≥80% after 100 cycles.

[0019] In this invention, based on the significant differences in the intrinsic diffusion capabilities of magnesium, niobium, and fluorine during heat treatment, the gradient transition layer, which is a spinel-like transition layer with gradient doping of magnesium, niobium, and fluorine from the inside to the outside, generally refers to the following trend: the concentration distribution of the gradient transition layer from the inside (near the substrate) to the outside (near the coating layer) follows the trend of "relative enrichment of magnesium → increase in niobium concentration → enrichment of fluorine at the outermost edge".

[0020] In this invention, the fluorine element in the gradient transition layer mainly plays the role of stabilizing the crystal structure, stabilizing the interface and inhibiting oxygen activity. By controlling its content, its corresponding performance can be further improved. In a preferred case, the fluorine content in the cathode material is 0.05-0.2 wt%, preferably 0.1-0.15 wt%.

[0021] In some preferred embodiments, the cathode material contains 0.05-0.2 wt% niobium and 0.3-0.7 wt% magnesium; more preferably, the cathode material contains 0.55-0.65 wt% niobium and 0.1-0.15 wt% magnesium.

[0022] In this invention, to further improve the electrochemical performance of the material, the diameter of the lithium cobalt oxide matrix is ​​preferably 2-10 μm, more preferably 4-8 μm, for example, it can be 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, or any value between these values.

[0023] According to the present invention, preferably, the specific surface area of ​​the lithium cobalt oxide matrix is ​​0.2-0.8 m².2 / g, preferably 0.4-0.6 m 2 / g, for example, can be 0.4 m 2 / g, 0.5 m 2 / g, 0.6 m 2 / g and the range between its values ​​and any other values.

[0024] In some preferred embodiments, the tap density of the lithium cobalt oxide matrix is ​​preferably 2.8-3.8 g / cm³. 3 Preferably, it is 3.0-3.5 m. 2 / g.

[0025] In this invention, the composite coating layer serves as an artificial CEI layer, effectively blocking direct contact between the electrolyte and the lithium cobalt oxide surface, and inhibiting HF corrosion and side reactions. The spinel-like transition layer enhances the bonding force between the composite coating layer and the substrate, preventing the composite coating layer from falling off. This dual protection significantly improves interface stability. To further enhance the synergistic effect between the two, in some preferred embodiments, the thickness of the transition layer is 100-400 nm, preferably 200-300 nm; in other preferred embodiments, the thickness of the composite coating layer is 10-40 nm, preferably 10-30 nm.

[0026] According to some preferred embodiments, the particle size of the nano-sized lithium niobate fluoride in the composite coating layer is 10-30 nm; according to other preferred embodiments, the particle size of the nano-sized magnesium oxide in the composite coating layer is 20-40 nm, preferably 25-30 nm, for example, it can be 25 nm, 28 nm, 30 nm, etc., or any range between these values.

[0027] A second aspect of the present invention provides a method for preparing a modified lithium cobalt oxide cathode material, the method comprising: S1: In the presence of a solvent, nano-lithium niobate, nano-magnesium oxide, fluorine source and lithium cobalt oxide are mixed and dried sequentially to prepare a composite precursor; S2: The composite precursor is calcined to prepare a modified lithium cobalt oxide cathode material.

[0028] In this invention, in order to prepare a cathode material with stable structure and excellent electrochemical performance, the amount of each component can be reasonably controlled. Therefore, in some preferred embodiments, based on the mass of the lithium cobalt oxide, the amount of nano-lithium niobate is 0.2-3 wt%, preferably 1-2 wt%; in other preferred embodiments, based on the mass of the lithium cobalt oxide, the amount of nano-magnesium oxide is 0.05-0.5 wt%, preferably 0.1-0.3 wt%.

[0029] According to the present invention, the fluorine source plays a dual synergistic role during the heat treatment process: the fluorine ions generated by its decomposition adsorb onto the surface of nanoparticles due to their high electronegativity, effectively inhibiting the aggregation of nanoparticles such as lithium niobate through electrostatic steric hindrance; simultaneously, the fluorine source component can undergo directional carbonization in situ, forming a conductive carbon network that tightly bridges and fixes the nanoparticles. The synergistic effect of these two factors ultimately constructs a continuous, dense, and firmly bonded composite coating layer on the surface of the cathode material. Preferably, the mass ratio of the fluorine source to the lithium niobate nanoparticles is 1:0.5-6, more preferably 1:2-4.

[0030] Within the above dosage range, a spinel-like transition layer (with a thickness of, for example, 100-400 nm, preferably 200-300 nm) with gradient doping of magnesium, niobium, and fluorine elements from the inside out can be formed on the surface of the lithium cobalt oxide substrate, as well as a continuous and dense composite coating layer with a thickness of about 10-40 nm, preferably 10-30 nm, which can ensure excellent interfacial lithium-ion transport dynamics while fully isolating the electrolyte.

[0031] In this invention, in a preferred embodiment, step S1 includes: grinding nano-lithium niobate and nano-magnesium oxide thoroughly and then placing them in a solvent for a first mixing treatment to obtain suspension I; then placing a fluorine source and lithium cobalt oxide into suspension I for a second mixing treatment to obtain intermediate II.

[0032] According to the present invention, the first mixing treatment may be performed by, for example, ultrasonic dispersion treatment. The preferred conditions for ultrasonic dispersion treatment are: power of 300-600W, temperature of 20-40℃, and time of 0.5-3 h; more preferably, the preferred conditions for ultrasonic dispersion treatment are: power of 400-500W, temperature of 25-35℃, and time of 1-2 h.

[0033] In this invention, the second mixing process can be, for example, magnetic stirring. The solvent is evaporated after the magnetic stirring process to obtain intermediate II. Preferably, the conditions for the magnetic stirring process are: temperature 60-80 ℃, time 4-10 h, and rotation speed 400-800 rpm. More preferably, the conditions for the magnetic stirring process are: temperature 70-75 ℃, time 6-8 h, and rotation speed 500-600 rpm.

[0034] In this invention, preferably, the solvent is selected from at least one of anhydrous ethanol, deionized water and ethylene glycol; the solid-liquid ratio of the solvent to the amount of nano-lithium niobate can be, for example, 1:50-250 g / mL, preferably 1:55-100 g / mL.

[0035] In this invention, the fluorine source serves not only to provide fluorine but also to act as a dispersant and binder. Accordingly, in a preferred embodiment, the fluorine source is selected from at least one of polyvinylidene fluoride, ammonium fluoride, and lithium fluoride.

[0036] According to the present invention, in a preferred embodiment, the drying conditions include 80-110 °C for 8-16 h; more preferably, the drying conditions include 90-100 °C for 12-15 h.

[0037] In this invention, preferably, step S1 further includes mechanically fusing the dried product to prepare a composite precursor; the conditions for the mechanical fusing are preferably: a rotation speed of 3500-5000 rpm, a temperature of 20-40 ℃, and a time of 10-30 min; more preferably, the conditions for the mechanical fusing are preferably: a rotation speed of 4000-4500 rpm, a temperature of 25-35 ℃, and a time of 15-20 min.

[0038] In some preferred embodiments, the nano-lithium niobate can be prepared by the following steps: LiNbO3 is mixed with anhydrous ethanol solution and then milled with zirconium beads (diameter can be, for example, 0.5-2 mm) under water cooling conditions (speed can be, for example, 3500-4500 r / min, time can be, for example, 45-50 h). After milling, it is dried (temperature can be, for example, 80-120 ℃, time can be, for example, 12-16 h) to obtain nano-lithium niobate (particle size preferably 10-30 nm).

[0039] In this invention, the calcination process in step S2 is the core step in driving and solidifying the formation of the gradient transition layer. At this time, the composite precursor decomposes, releasing active Nb, Mg, F, and other ions. These ions have different diffusion coefficients, and this difference in diffusion rate directly leads to a natural gradient distribution of element concentration and type from the surface to the interior, thereby obtaining a spinel-like transition layer with gradient doping of magnesium, niobium, and fluorine elements from the inside out.

[0040] According to the present invention, in a preferred embodiment, in step S2, the calcination treatment conditions include: a heating rate of 3-8℃ / min, a temperature of 400-1100℃, and a time of 0.5-3 h; more preferably, the calcination treatment conditions include: a heating rate of 4-6℃ / min, a temperature of 700-900℃, and a time of 1-2 h.

[0041] A third aspect of the present invention provides a modified lithium cobalt oxide cathode material prepared by the preparation method described in the second aspect of the present invention.

[0042] A fourth aspect of the present invention provides a lithium-ion battery in which the positive electrode comprises the modified lithium cobalt oxide positive electrode material described in the first aspect of the present invention.

[0043] According to the present invention, the preparation of the positive electrode sheet may include the following steps: (1) The modified lithium cobalt oxide cathode material, conductive agent and binder provided by the present invention are mixed in a mass ratio of 6-10:1:1 (preferably 7-9:1:1), and then N-methylpyrrolidone solvent is added and stirred and mixed evenly to obtain cathode slurry; (2) The positive electrode slurry is uniformly coated on the surface of the positive electrode current collector (such as aluminum foil), dried, rolled and cut to obtain the positive electrode sheet.

[0044] The conductive agent may be selected from one or more of conductive carbon black, acetylene black, Ketjen black, carbon nanotubes or graphene; the binder may be selected from one or more of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polytetrafluoroethylene, etc.

[0045] According to the present invention, the preparation process of the lithium-ion battery may include: using the positive electrode as the positive electrode, using a lithium metal sheet as the negative electrode, using a polyolefin microporous membrane (preferably an Al2O3 coated polyethylene membrane) as the separator, and assembling it together with the electrolyte to form a battery cell, which is then packaged and formed to obtain the lithium-ion battery.

[0046] The electrolyte can be a non-aqueous electrolyte formed by dissolving lithium salt in an organic solvent, such as 1M LiPF6 dissolved in a mixed solvent (e.g., ethylene carbonate (EC) and dimethyl carbonate (EMC) in a volume ratio of 1:1-2).

[0047] Through the above technical solution, the lithium-ion battery made using the cathode material described in this invention exhibits excellent comprehensive electrochemical performance at a high voltage of 3.0-4.6 V. In a preferred embodiment, the first-cycle discharge specific capacity of the battery is not less than 200 mA hg. -1 After 100 cycles at a 0.5C rate, the capacity retention is higher than 80%.

[0048] The present invention will be described in detail below through embodiments.

[0049] In the following examples, nano-magnesium oxide was purchased from Alfaisa Chemicals Ltd., with a particle size of 30 nm; lithium cobalt oxide was purchased from Tianjin Guoan Mengguli New Material Technology Co., Ltd., with a particle size of 5 μm and a specific surface area of ​​0.5 m². 2 / g, tap density is 3.3 g / cm³ 3 ; The nano-lithium niobate was prepared by the following method: 20 g of LiNbO3 was mixed with 500 mL of anhydrous ethanol solution and then milled with zirconium beads (1 mm in diameter) under water cooling conditions (4000 r / min for 48 h). After milling, the mixture was dried (100 ℃ for 14 h) to obtain nano-lithium niobate 1# with a particle size of 10 nm.

[0050] Example 1 This embodiment illustrates a method for preparing modified lithium cobalt oxide cathode materials, including: S1: At room temperature (25℃, the same below), 3 g of nano lithium niobate 1# and 0.5 g of nano magnesium oxide were thoroughly ground, and then 200 mL of anhydrous ethanol was added for ultrasonic dispersion treatment for 1 h (power of 500 W) to obtain suspension I1; 1.5 g of polyvinylidene fluoride and 300 g of lithium cobalt oxide were added to suspension I1, and the mixture was placed on a constant temperature magnetic stirrer and stirred at 70 °C for 8 h (500 rpm). Then it was dried in an oven at 100 °C for 12 h, and then mechanically fused at 4000 rpm for 20 min to obtain composite precursor 1#. S2: In the presence of air, the composite precursor 1# obtained in step S1 is calcined for 1 hour (heated to 850 ℃ at a heating rate of 5 ℃ / min) to obtain the modified lithium cobalt oxide cathode material 1#. Among them, the thickness of the gradient transition layer is 200 nm, as determined by high-resolution transmission electron microscopy and etching XPS; the thickness of the composite coating layer is 15 nm.

[0051] Example 2 This embodiment illustrates a method for preparing modified lithium cobalt oxide cathode materials, including: S1: At room temperature (25℃, the same below), 3.6 g of nano lithium niobate 1# and 0.8 g of nano magnesium oxide were thoroughly ground, and then 200 mL of anhydrous ethanol was added for ultrasonic dispersion treatment for 1.5 h (power of 500 W) to obtain suspension I2; 1.8 g of polyvinylidene fluoride and 300 g of lithium cobalt oxide were added to suspension I2, placed on a constant temperature magnetic stirrer and stirred at 75 °C for 7.5 h (600 rpm), then transferred to a 95 °C oven for drying for 15 h, and then mechanically fused at 4500 rpm for 15 min to obtain composite precursor 2#. S2: In the presence of air, the composite precursor 2# obtained in step S1 is calcined for 1.2 h (heated to 800 ℃ at a heating rate of 5 ℃ / min) to obtain the modified lithium cobalt oxide cathode material 2#.

[0052] Example 3 Following a similar method to Example 1, except that 0.5 g of polyvinylidene fluoride was used instead of 1.5 g of polyvinylidene fluoride, and the remaining steps were the same as in Example 1, the modified lithium cobalt oxide cathode material 3# was prepared.

[0053] Example 4 Following a similar method to Example 1, except that 2 g of polyvinylidene fluoride was used instead of 1.5 g of polyvinylidene fluoride, and the remaining steps were the same as in Example 1, the modified lithium cobalt oxide cathode material 4# was prepared.

[0054] Example 5 Following a similar method to Example 1, except that step S2 involves calcining the composite precursor 1# obtained in step S1 for 1 h in the presence of air (heating to 650 ℃ at a heating rate of 5 ℃ / min), with the remaining steps being the same as in Example 1, to prepare the modified lithium cobalt oxide cathode material 5#.

[0055] Example 6 Following a similar method to Example 1, except that step S2 involves calcining the composite precursor 1# obtained in step S1 for 1 h in the presence of air (heating to 1050 ℃ at a heating rate of 5 ℃ / min), with the remaining steps being the same as in Example 1, to prepare the modified lithium cobalt oxide cathode material 6#.

[0056] Example 7 Following a similar method to Example 1, except that 1.5g of nano-lithium niobate 1# was used instead of 3g of nano-lithium niobate 1#, and the remaining steps were the same as in Example 1, the modified lithium cobalt oxide cathode material 7# was prepared.

[0057] Example 8 Following a similar method to Example 1, except that 0.9 g of nano-magnesium oxide was used instead of 0.5 g of nano-magnesium oxide, and the remaining steps were the same as in Example 1, the modified lithium cobalt oxide cathode material 8# was prepared.

[0058] Comparative Example 1 Unmodified lithium cobalt oxide was used as the cathode material 1'#.

[0059] Comparative Example 2 Following a similar method to Example 1, except that step S1 does not involve adding polyvinylidene fluoride, the following steps are performed: at room temperature, 3 g of nano lithium niobate 1# and 0.5 g of nano magnesium oxide are thoroughly ground, and then 200 mL of anhydrous ethanol is added for ultrasonic dispersion treatment for 1 h (power of 500 W) to obtain suspension I'2. 300 g of lithium cobalt oxide was added to suspension I'2, placed on a constant temperature magnetic stirrer and stirred at 70 ℃ for 8 h, then transferred to a 100 ℃ oven for drying for 12 h, and then mechanically fused at 4000 rpm for 20 min to obtain composite precursor 2'#. The remaining steps are the same as in Example 1, and the modified lithium cobalt oxide cathode material 2'# is prepared.

[0060] Comparative Example 3 Following a similar method to Example 1, except that step S1 does not involve adding nano-magnesium oxide, it includes: at room temperature, 3 g of nano-lithium niobate 1# and 1.5 g of polyvinylidene fluoride are thoroughly ground, and then 200 mL of anhydrous ethanol is added for ultrasonic dispersion treatment for 1 h (power of 500 W) to obtain suspension I'3. 300 g of lithium cobalt oxide was added to suspension I'3, placed on a constant temperature magnetic stirrer and stirred at 70 ℃ for 8 h, then transferred to a 100 ℃ oven for drying for 12 h, and then mechanically fused at 4000 rpm for 20 min to obtain composite precursor 3'#. The remaining steps are the same as in Example 1, and the modified lithium cobalt oxide cathode material 3'# is prepared.

[0061] Test Example 1 This test case is used for: (1) The content ratio of each element on the surface of the modified lithium cobalt oxide cathode material prepared in the examples and comparative examples is shown in Table 1. The testing methods include: scanning the surface of the material using EDS testing to obtain the weight percentage of each element (based on the total mass of the modified lithium cobalt oxide cathode material). (2) The surface morphology of the modified lithium cobalt oxide cathode materials prepared in Example 1, Comparative Example 1 and Comparative Example 2 was observed using a transmission electron microscope (TEM, JEM-2100, Nippon Electronics Corporation). The results are as follows: Figure 1 As shown; The microstructure of Example 1 was further characterized using high-resolution transmission electron microscopy, and a fast Fourier transform was performed on selected regions to obtain electron diffraction patterns reflecting local lattice information. The results are as follows: Figure 2 As shown; (3) X-ray diffraction (XRD) was used to analyze the phase composition of the modified lithium cobalt oxide cathode materials prepared in Example 1, Comparative Example 1, and Comparative Example 2 using a PANalytical Empyrean X-ray diffractometer with a scanning range of 10°-90°. The diffraction patterns are shown in the figure below. Figure 3 As shown; Table 1

[0062] according to Figure 1 It is known that different modification treatments directly affect the surface morphology of the cathode material. In Example 1, the dispersion and carbonization of PVDF effectively inhibited the agglomeration of nano-coated particles, forming a uniform and dense composite coating layer, which avoided the local agglomeration in Comparative Example 2. This demonstrates the superiority of the fluorinated composite coating process in optimizing the surface morphology of the material and improving its structural integrity, laying a structural foundation for improving electrochemical performance.

[0063] Depend on Figure 2 It can be seen that Example 1 successfully constructed a multi-level composite structure of "composite coating layer - spinel-like doped layer - layered bulk phase". The synergistic effect of the three-level structure solves the problems of weak interfacial bonding and poor structural stability in traditional single modification methods, and provides structural support for the long-cycle stability and high-rate performance of the material.

[0064] according to Figure 3 It can be seen that, compared with the comparative example, the (003) peak in Example 1 has the largest low-angle shift, indicating that Nb 5+ With F - The electrostatic repulsion effectively widens the lithium interlayer spacing, providing a smoother channel for lithium-ion transport; the sharp and symmetrical peak shape indicates good crystallinity and no lattice distortion. These results confirm the positive effect of multi-element doping on optimizing lattice parameters.

[0065] Test Example 2 This test example is used to test the electrochemical performance of lithium-ion batteries, as detailed in Table 2. Figures 4-6 As shown; The above-mentioned lithium-ion battery was prepared using the modified lithium cobalt oxide cathode material obtained in the examples and comparative examples, including: (1) The positive electrode material, conductive acetylene black and polyvinylidene fluoride obtained in the examples and comparative examples were mixed in an appropriate amount of N-methylpyrrolidone solvent according to a mass ratio of 8:1:1 to obtain the positive electrode slurry. (2) The positive electrode slurry is coated on aluminum foil as the positive electrode of the battery, lithium sheet is used as the negative electrode of the battery, polyethylene film coated with Al2O3 is used as the separator, and 8335 electrolyte (1M LiPF6 dissolved in a solvent with a volume ratio of 1:1 ethylene carbonate (EC): dimethyl carbonate (EMC)) is used as the electrolyte to assemble lithium-ion battery 1#. The specific capacity curves of the batteries in Example 1, Comparative Example 1, and Comparative Example 2 during long-cycle discharge at a voltage range of 3.0-4.6 V and a rate of 0.5C are shown below. Figure 4 As shown; The discharge specific capacity of the batteries in Example 1, Comparative Example 1, and Comparative Example 2 at different discharge rates (0.1C, 0.2C, 0.5C, 1C, 2C, 5C) within the 3.0-4.6 V voltage range is as follows: Figure 5 As shown; The lithium-ion diffusion coefficients calculated for Example 1 and Comparative Example 1 based on the results of galvanostatic intermittent titration (GITT) tests after the first week and 100 cycles are as follows: Figure 6 As shown; Test method: Cycling performance: Performed at room temperature (25℃), with a charge / discharge voltage of 3.0V-4.6V, a charge rate of 0.5C, and a discharge rate of 0.5C; Rate performance: Charge and discharge tests were performed sequentially at rates of 0.1C, 0.2C, 0.5C, 1C, 2C, and 5C.

[0066] Table 2

[0067] Figure 4 Example 1 demonstrates excellent long-term cycling stability. By suppressing electrolyte erosion and harmful phase transitions through a fluorinated composite coating layer and combining it with multi-element doping to stabilize lattice oxygen, Example 1 effectively solves the problem of rapid capacity decay in Comparative Example 1. The capacity of Example 1 tends to stabilize in the later stages of cycling, which confirms the dynamic optimization effect of the CEI layer and provides performance support for the long-term application of the material under high pressure.

[0068] Depend on Figure 5 It is evident that the multi-level structure and widened lithium-ion transport channels of Example 1 significantly reduce ion migration resistance, maintaining a high discharge specific capacity even at high rates, which is significantly superior to the comparative examples. This also confirms the technical advantages of this modification process in improving the high-current charge and discharge capability of materials, meeting the application requirements of high-power devices.

[0069] according to Figure 6 It can be seen that the lithium-ion diffusion coefficient of Example 1 is significantly higher than that of Comparative Example 1, confirming the synergistic effect of fluorinated composite coating and multi-element doping on optimizing ion transport kinetics. After 100 cycles, the diffusion coefficient of Example 1 slightly increased, reflecting the dynamic optimization effect of the CEI layer, while the diffusion coefficient of Comparative Example 1 decreased significantly, reflecting the serious obstacle of structural collapse to ion transport, further corroborating the effectiveness of the modification process of Example 1 in improving kinetic stability.

[0070] As can be seen from Table 2, compared with the comparative example, the embodiments of the present invention have significantly superior electrochemical performance, and can simultaneously achieve high specific capacity and cycle performance. In particular, in Examples 1 and 2, the first-cycle discharge specific capacity of the battery is not less than 200 mA hg. -1Furthermore, after 100 cycles at a 0.5C rate, the capacity retention rate is higher than 90%.

[0071] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A modified lithium cobalt oxide cathode material, characterized in that, The material comprises a lithium cobalt oxide matrix and a gradient transition layer and a composite coating layer sequentially coated on the outer surface of the lithium cobalt oxide matrix; The gradient transition layer consists of a spinel-like transition layer with gradient doping of magnesium, niobium, and fluorine elements from the inside out; the composite coating layer contains nano-sized lithium fluorinated niobate and nano-sized magnesium oxide.

2. The cathode material according to claim 1, wherein, The diameter of the lithium cobalt oxide substrate is 2-10 μm, preferably 4-8 μm; and / or the specific surface area of the lithium cobaltate matrix is 0.2 to 0.8 m 2 / g, preferably 0.4 to 0.6 m 2 / g; and / or the tap density of the lithium cobalt oxide base is 2.8-3.8 g / cm3 3 , preferably 3.0-3.5 m 2 / g.

3. The positive electrode material according to claim 1 or 2, wherein The fluorine content in the cathode material is 0.05-0.2 wt%, preferably 0.1-0.15 wt%.

4. The positive electrode material according to claim 1 or 2, wherein The cathode material contains 0.05-0.2 wt% niobium and 0.3-0.7 wt% magnesium. Preferably, the cathode material contains 0.55-0.65 wt% niobium and 0.1-0.15 wt% magnesium.

5. A method for preparing a modified lithium cobalt oxide cathode material, characterized in that, The method includes: S1: In the presence of a solvent, nano-lithium niobate, nano-magnesium oxide, fluorine source and lithium cobalt oxide are mixed and dried sequentially to prepare a composite precursor; S2: The composite precursor is calcined to prepare a modified lithium cobalt oxide cathode material.

6. The production method according to claim 5, wherein Based on the mass of the lithium cobalt oxide used, the amount of nano-lithium niobate used is 0.2-3 wt%, preferably 1-2 wt%; And / or, based on the mass of the lithium cobalt oxide used, the amount of nano-magnesium oxide used is 0.05-0.5 wt%, preferably 0.1-0.3 wt%; And / or, the mass ratio of the fluorine source to the amount of nano-lithium niobate is 1:0.5-6, preferably 1:2-4.

7. The production method according to claim 5 or 6, wherein In step S1, the solvent is selected from at least one of anhydrous ethanol, deionized water, and ethylene glycol; And / or, the fluorine source is selected from at least one of polyvinylidene fluoride, ammonium fluoride and lithium fluoride; And / or, the drying conditions include: 80-110 °C for 8-16 h.

8. The production method according to claim 5 or 6, wherein In step S2, the calcination conditions include: a heating rate of 3-8 ℃ / min, a temperature of 400-1100 ℃, and a time of 0.5-3 h; Preferably, the calcination treatment conditions include: a heating rate of 4-6 ℃ / min, a temperature of 700-900 ℃, and a time of 1-2 h.

9. A modified lithium cobalt oxide cathode material prepared by the method according to any one of claims 5-8.

10. A lithium-ion battery, wherein, The positive electrode of the battery contains the modified lithium cobalt oxide positive electrode material as described in any one of claims 1-4.

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