A high-voltage lithium cobalt oxide cathode material and a preparation method thereof

Abstract

The application relates to the technical field of lithium ion batteries, in particular to a high-voltage lithium cobaltate positive electrode material and a preparation method thereof. The technical scheme of the application comprises the chemical composition of the positive electrode material, wherein the positive electrode material is selected from at least two elements of Al, Mg, Ti and Zr, and the content of the element is 0.01-0.1, 0.01-0.1 and 0.01-0.1 respectively. Through the triple strategy of multi-element synergistic doping, core-shell structure design and surface defect regulation, the performance of the high-voltage lithium cobaltate positive electrode material is remarkably improved. In particular, through the synergistic effect of the specific element combination Al+Mg+Ti and the coupling effect of the gradient distribution of the F element and the nano-defect structure, the structural phase transition and the interface side reaction in the high-voltage cycle process are effectively inhibited, and the cycle life and the thermal stability of the material are significantly improved.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a high-voltage lithium cobalt oxide cathode material and its preparation method. Background Technology

[0002] Lithium-ion batteries are widely used in portable electronic devices, electric vehicles, and energy storage systems due to their advantages such as high energy density, long cycle life, and no memory effect. Lithium cobalt oxide (LiCoO2), as the earliest commercially available cathode material for lithium-ion batteries, remains the mainstream cathode material in consumer electronics due to its stable structure, flat charge / discharge plateau, and mature manufacturing process. However, the actual specific capacity of traditional lithium cobalt oxide materials is typically only 140-160 mAh / g, far lower than its theoretical specific capacity (274 mAh / g), making it difficult to meet the demands of next-generation high-energy-density batteries.

[0003] Increasing the charging cutoff voltage of lithium cobalt oxide materials (e.g., from 4.2V to above 4.5V) is an effective way to improve their specific capacity. When the charging voltage is higher than 4.35V, With increased extraction yield, the specific capacity of the material can exceed 200 mAh / g. However, lithium cobalt oxide materials face the following prominent problems under high pressure conditions:

[0004] Decreased structural stability: Under deep delithiation state, Increased content can easily trigger lattice oxygen precipitation, causing the material to transform from a layered structure to a spinel or rock salt phase, resulting in irreversible capacity loss.

[0005] Exacerbated interfacial side reactions: Under high voltage, the electrolyte undergoes oxidative decomposition on the surface of the positive electrode material. The generated acidic substances such as HF corrode the positive electrode material, dissolve Co elements and migrate to the negative electrode, leading to increased battery internal resistance and deterioration of cycle performance.

[0006] Deterioration in thermal stability: Lithium cobalt oxide materials under high pressure are prone to violent exothermic reactions in high-temperature environments, which can lead to battery thermal runaway and pose safety hazards.

[0007] To solve the above problems, existing technologies mainly employ the following methods:

[0008] Element doping: By introducing metallic elements such as Al, Mg, and Ti or non-metallic elements such as F and P, the structural stability or interface stability of the material is improved.

[0009] Surface coating: A protective layer such as oxides (e.g., Al2O3, ZrO2), fluorides (e.g., LiF), or phosphates (e.g., AlPO4) is coated on the material surface to inhibit electrolyte corrosion;

[0010] Morphology control: Optimize lithium-ion diffusion pathways by controlling the particle morphology, particle size distribution, or specific surface area of ​​the material.

[0011] However, existing technologies still have the following shortcomings: the effect of single-element doping is limited, and excessive doping may reduce the electronic / ionic conductivity of the material; the surface coating layer may increase interfacial impedance, affecting the rate performance of the battery; under high voltage, material structural degradation and interfacial side reactions mutually promote each other; and single modification methods are difficult to achieve long-term stability. Therefore, developing a technical solution that can simultaneously solve the problems of structural stability, interfacial compatibility, and thermal stability of high-voltage lithium cobalt oxide materials is of significant practical importance. Summary of the Invention

[0012] The purpose of this invention is to address the problems of poor structural stability, interface compatibility, and thermal stability of existing high-voltage lithium cobalt oxide materials in the background art, and to propose a high-voltage lithium cobalt oxide cathode material and its preparation method.

[0013] In a first aspect, this application provides a high-voltage lithium cobalt oxide cathode material, the chemical composition of which is as follows: ,in, It consists of at least two elements selected from Al, Mg, Ti, and Zr. , , ;

[0014] The cathode material has a core-shell structure, with the core being a lithium-rich lithium cobalt oxide phase and the outer shell being a lithium-containing... Composite oxide layers of elements;

[0015] The outer shell The content of elements gradually increases from the inside out, and The concentration of the element in the shell gradually decreases from the inside to the outside; the shell The elemental content increases 1.5-3 times from the inner layer to the outer layer. The element content decreases by 30%-60% from the inner layer to the outer layer;

[0016] The primary particle surface of the cathode material has a nanoscale oxygen vacancy defect structure, in which uniformly dispersed oxygen vacancy defects are distributed. The element, and the depth of the oxygen vacancy defect is 5-50 nm.

[0017] Through the above scheme, the synergistic effect of at least two elements selected from Al, Mg, Ti, and Zr can enhance the structural stability of the material and suppress cation mixing, which is better than that of a single element. In the core-shell structure, the lithium-rich core ensures high capacity, while the composite oxide layer containing elements in the shell can block electrolyte erosion. Moreover, the element content gradient in the shell increases, which optimizes the interface performance. The nanoscale defect structure on the surface of the primary particles provides a fast diffusion channel for lithium ions and further enhances the structural stability due to the uniform distribution of elements. The synergy of multiple factors makes the material perform better under high pressure.

[0018] Optionally, the The elements are a combination of Al and Mg, where the molar content of Al is... The molar content of Mg is ,and .

[0019] Optionally, the The elements are a combination of Al, Mg, and Ti, with the molar content of Al being [missing information]. The molar content of Mg is The molar content of Ti is ,and .

[0020] Optionally, in the core-shell structure, the core occupies 70% to 90% of the total particle volume, and the outer shell has a thickness of 50-200 nm.

[0021] Optionally, the specific surface area of ​​the positive electrode material is 0.2-0.8 m². 2 / g, tap density is 2.8-3.4g / cm³ 3 .

[0022] Secondly, this application provides a method for preparing a high-voltage lithium cobalt oxide cathode material as described in the first aspect, comprising the following steps:

[0023] Preparation of precursors: cobalt salt, Salts of the element are prepared into a mixed solution according to stoichiometric ratio, and a precipitating agent is added to carry out a coprecipitation reaction to obtain a solution containing... Cobalt hydroxide precursor of element;

[0024] Lithification process: The precursor is mixed with a lithium source and subjected to a first high-temperature sintering in an oxygen atmosphere to obtain the lithiation product;

[0025] Surface fluorination treatment: The lithium-ion product is mixed with a fluorine source and subjected to a second high-temperature sintering in an inert atmosphere. The temperature of the second high-temperature sintering is lower than that of the first high-temperature sintering.

[0026] Defect structure manipulation: The surface-fluorinated product is subjected to low-temperature annealing in an oxygen-containing atmosphere to form the nanoscale defect structure. This low-temperature annealing, performed in an oxygen-containing atmosphere, induces the release of oxygen from the surface lattice, forming oxygen vacancy defects, and simultaneously promotes… Elements migrate into oxygen vacancies and disperse uniformly.

[0027] It is worth noting that the co-precipitation method for preparing the precursor allows for uniform mixing of cobalt salts and M element salts, ensuring uniform dispersion of M element in subsequent materials. This lays the foundation for multi-element synergistic effects and avoids the uneven element distribution problems that may occur with traditional mixing methods. This invention optimizes the crystal structure. The first high-temperature sintering is performed in an oxygen atmosphere, which is conducive to the formation of a stable layered structure. The lithium-rich core can improve the specific capacity of the material. The second high-temperature sintering temperature is lower than the first, achieving surface fluorination while avoiding damage to the already formed core structure. Simultaneously, it allows the F element in the shell to form a gradient distribution that gradually increases from the inside out, enhancing surface stability. Furthermore, the low-temperature annealing treatment, performed in an oxygen-containing atmosphere, can precisely control the formation of nanoscale defect structures on the surface of the primary particles. These defects not only provide rapid diffusion channels for lithium ions but also allow for uniform distribution of M element, further strengthening structural stability and ion transport capabilities. This is one of the key processes for achieving high-performance materials.

[0028] Optionally, the temperature of the first high-temperature sintering is 850-950℃, and the holding time is 8-15 hours; the temperature of the second high-temperature sintering is 600-750℃, and the holding time is 4-8 hours; the temperature of the low-temperature annealing treatment is 300-500℃, and the holding time is 2-6 hours.

[0029] Based on the above scheme and the diffusion behavior of F element, during the second sintering, the fluorine source and the lithium-ion product (Li) 1+ x Co 1-y M y An interfacial reaction will occur at the surface contact area of ​​O2, F - Ions diffuse from the surface inwards. Because the second sintering temperature (600-750℃) is lower than the first lithiation sintering temperature (850-950℃), the internal crystal structure of the material has already formed a stable rigid framework during the high-temperature lithiation stage, significantly increasing the atomic diffusion activation energy. - Ions have difficulty penetrating the core. However, the outer shell region, being on the material's surface, has relatively more lattice defects and is in direct contact with the fluorine source, allowing for limited F generation even at lower temperatures. - Ion displacement reaction (substitution of O) 2- (sites), forming an F-containing composite oxide layer.

[0030] At high temperatures, F⁻ ions have strong diffusion capabilities. If the second sintering temperature is close to or exceeds that of the first, F⁻ ions will diffuse more rapidly. - It is possible that a large amount of it will penetrate into the core, resulting in a uniform distribution; while lower temperatures will suppress F. - Deep diffusion into the interior leads to the enrichment of fluorine (F) in the surface layer due to the continuous supply of fluorine, forming a concentration gradient from the surface to the subsurface. Experimental characterization (such as X-ray photoelectron spectroscopy depth profiling) verifies this gradient: the atomic percentage of F in the outer shell is significantly higher than that in the inner layer, and the F content decreases rapidly after 50 nm from the surface inward, showing a clear difference from the F content in the core region. This is completely consistent with the kinetic characteristics of diffusion restriction at low temperatures.

[0031] Furthermore, the lithium-rich core formed during the first high-temperature sintering exhibits high structural stability, and the lattice integrity of the core remains unaffected during the second low-temperature sintering, with only the outer shell experiencing localized F2O2. - Doping and reconstruction further reinforce the gradient distribution characteristic of "high F on the surface and low F inside". This gradient design avoids F - Excessive doping blocks the lithium-ion insertion / extraction channels in the core, while the high F content on the surface enhances the corrosion resistance to the electrolyte, achieving a balance between structural stability and ion conductivity.

[0032] Optionally, the fluorine source is , , At least one of them, and the amount of fluorine source added is 0.5% to 3% of the mass of the lithiation product.

[0033] Optionally, the lithium source is at least one of lithium carbonate and lithium hydroxide, and the molar ratio of the lithium source to the metal element in the precursor is 1.01:1 to 1.05:1.

[0034] Optionally, the precipitant is a mixed solution of sodium hydroxide and ammonia, the pH value of the coprecipitation reaction is controlled at 10.5-12.0, and the reaction temperature is 40-60℃.

[0035] Compared with the prior art, this application includes at least one of the following beneficial technical effects:

[0036] By forming complementary effects through multi-element synergistic doping, Al enhances structural rigidity, Mg reduces cation mixing, and Ti improves electronic conductivity, achieving synergistic effects that far exceed those of single-element doping.

[0037] By combining a core-shell structure with gradient fluorine doping, the core ensures high capacity, the shell blocks electrolyte corrosion, and the gradient distribution of fluorine reduces the obstruction of lithium-ion diffusion and reduces HF corrosion, thus slowing down the increase of interface impedance at high voltages above 4.5V and delaying performance degradation.

[0038] The surface nanoscale defect structure provides a fast diffusion channel for lithium ions, improving rate performance. It can also adsorb harmful products from electrolyte decomposition, reduce damage to the main material, and ensure high lithium ion diffusion coefficient and stable capacity output after long-term cycling.

[0039] It exhibits excellent performance under high voltage, with a specific capacity exceeding 200mAh / g at a cutoff voltage of 4.5V and a capacity retention rate exceeding 85% after 1000 cycles at 1C, meeting the requirements for high energy density. Furthermore, the thermal decomposition initiation temperature is increased by more than 50℃, reducing the risk of thermal runaway.

[0040] This invention achieves a breakthrough improvement in the performance of high-voltage lithium cobalt oxide cathode materials through a triple strategy of multi-element synergistic doping, core-shell structure design, and surface defect control. In particular, through the synergistic effect of a specific element combination of Al+Mg+Ti and the coupling effect of gradient-distributed F elements with nano-defect structures, structural phase transitions and interfacial side reactions during high-voltage cycling are effectively suppressed, significantly improving the cycle life and thermal stability of the material. Attached Figure Description

[0041] Figure 1 This is a flowchart of a method for preparing a high-voltage lithium cobalt oxide cathode material. Detailed Implementation

[0042] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0043] Example 1

[0044] This invention proposes a high-voltage lithium cobalt oxide cathode material: The cathode material has a core-shell structure, with the core accounting for 80% of the total particle volume and the outer shell being 100 nm thick. The F element content in the outer shell increases by 2 times from the inner layer to the outer layer, while the total Al and Mg element content decreases by 45% from the inner layer to the outer layer. The primary particle surface has a nanoscale oxygen vacancy defect structure with a defect depth of 20 nm, and Al and Mg elements are uniformly dispersed in the oxygen vacancy defects.

[0045] It should be noted that the defect depth was measured using high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) combined with energy dispersive spectroscopy (EDS). HAADF-STEM can directly observe the microstructure from the surface to the interior of the material through atomic number contrast imaging; EDS can accurately analyze elemental distribution, and oxygen vacancy regions will exhibit characteristic signal changes due to the lack of oxygen. The specific calculation steps are as follows:

[0046] The primary particles of the cathode material are subjected to ultrathin cross-sections (50-100 nm thick) to obtain cross-sectional samples along the radial direction of the particles.

[0047] High-resolution imaging of particle surface regions was performed using HAADF-STEM to identify lattice distortion regions formed by oxygen vacancies (defect regions show contrast differences with normal lattice regions).

[0048] By combining the EDS line scan mode, the oxygen content is scanned point by point from the particle surface to the interior: the oxygen signal in the defect region will be significantly lower than that in the normal lattice region. When the oxygen content recovers to the normal lattice level, the distance between this position and the surface is the defect depth.

[0049] The final defect depth is obtained by statistically analyzing different cross-sections of multiple particles and taking the average value.

[0050] Preparation method as follows Figure 1 As shown:

[0051] Step 1: Precursor Preparation

[0052] A mixed solution with a total concentration of 2.0 mol / L was prepared by mixing Co(NO3)2•6H2O, Al(NO3)3•9H2O, and Mg(NO3)2•6H2O in a molar ratio of Co:Al:Mg = 0.94:0.03:0.03.

[0053] Prepare a precipitant solution containing 4.0 mol / L NaOH and 2.0 mol / L NH3•H2O;

[0054] At 50℃ and pH=11.5, the mixed solution and the precipitant solution were added to the reactor in parallel flow, while nitrogen gas was introduced for protection. The stirring speed was 500 rpm, and the reaction was carried out for 12 hours.

[0055] After the reaction was completed, the sample was filtered, washed, and dried to obtain a spherical Al and Mg co-doped cobalt hydroxide precursor.

[0056] Step 2: Lithification treatment

[0057] The precursor was mixed with Li₂CO₃ at a molar ratio of Li / (Co+Al+Mg) = 1.05:1, and heated to 920℃ at a rate of 5℃ / min in an oxygen atmosphere, held at that temperature for 12 hours, and then cooled in the furnace. The mixture was then crushed and sieved to obtain the lithiation product. ;

[0058] Step 3: Surface fluorination treatment

[0059] The lithiation product was mixed with LiF at a mass ratio of 100:1.5, heated to 700℃ at 3℃ / min in an argon atmosphere, held at that temperature for 6 hours, and then cooled with the furnace. The mixture was then crushed and sieved to obtain the surface fluorination product. This process creates an increasing concentration gradient of F element in the shell from the inside out, while simultaneously promoting the migration of Al and Mg elements towards the core, creating a decreasing gradient.

[0060] Step 4: Defect Structure Control

[0061] The fluorinated product was heated to 400°C in air at a rate of 2°C / min and held for 4 hours. It was then cooled in the furnace. The product was sieved to obtain the final product. Low-temperature annealing treatment induced the release of oxygen from the surface lattice, forming oxygen vacancy defects with a depth of 20 nm. At the same time, it promoted the migration of Al and Mg elements into the oxygen vacancy and uniformly dispersed them.

[0062] Example 2

[0063] High-voltage lithium cobalt oxide cathode material: The cathode material has a core-shell structure, with the core accounting for 75% of the total particle volume and the outer shell thickness being 150 nm. The F element content in the outer shell increases threefold from the inner layer to the outer layer, while the total content of Al, Mg, and Ti elements decreases by 60% from the inner layer to the outer layer. The primary particle surface has a nanoscale oxygen vacancy defect structure with a defect depth of 50 nm (the calculation method is the same as in Example 1), and Al, Mg, and Ti elements are uniformly dispersed in the oxygen vacancy defects.

[0064] Step 1: Precursor Preparation

[0065] A mixed solution with a total concentration of 1.8 mol / L was prepared by mixing CoSO4•7H2O, Al2(SO4)3•18H2O, MgSO4•7H2O, and Ti(SO4)2 in a molar ratio of Co:Al:Mg:Ti = 0.92:0.03:0.03:0.02.

[0066] Prepare a precipitant solution containing 3.5 mol / L NaOH and 1.8 mol / L NH3•H2O;

[0067] At 45℃ and pH=11.0, the mixed solution and the precipitant solution were added to the reactor in parallel flow, while nitrogen gas was introduced for protection. The stirring speed was 600 rpm, and the reaction was carried out for 10 hours.

[0068] After the reaction was completed, the sample was filtered, washed, and dried to obtain a spherical Al, Mg, and Ti co-doped cobalt hydroxide precursor.

[0069] Step 2: Lithification treatment

[0070] The precursor was mixed with LiOH•H2O at a molar ratio of Li / (Co+Al+Mg+Ti)=1.01:1, heated to 880℃ at 4℃ / min in an oxygen atmosphere, held for 10 hours, and then cooled in the furnace.

[0071] Crushing and sieving yielded lithiation products. .

[0072] Step 3: Surface fluorination treatment

[0073] The lithium-ion product was mixed with NH4F at a mass ratio of 100:1.0, heated to 650°C at 2°C / min in a nitrogen atmosphere, held at that temperature for 5 hours, and then cooled in the furnace.

[0074] Crushing and sieving yields surface fluorinated products. .

[0075] Step 4: Defect Structure Control

[0076] The fluorinated product was heated to 350°C at 1°C / min in an oxygen atmosphere, held at that temperature for 3 hours, and then cooled in the furnace. The product was then sieved to obtain the final product. This process creates an increasing concentration gradient of F element in the shell from the inside out, while simultaneously promoting the migration of Al, Mg, and Ti elements towards the core to create a decreasing gradient.

[0077] Example 3

[0078] High-voltage lithium cobalt oxide cathode material: The cathode material has a core-shell structure, with the core accounting for 90% of the total particle volume and the outer shell thickness being 50 nm. The F element content in the outer shell increases by 1.5 times from the inner layer to the outer layer, while the total content of Al, Mg, and Ti elements decreases by 30% from the inner layer to the outer layer. The primary particle surface has a nanoscale oxygen vacancy defect structure with a defect depth of 5 nm (the calculation method is the same as in Example 1), and Al, Mg, and Ti elements are uniformly dispersed in the oxygen vacancy defects.

[0079] Step 1: Precursor Preparation

[0080] A mixed solution with a total concentration of 2.2 mol / L was prepared by mixing Co(NO3)2•6H2O, Al(NO3)3•9H2O, Mg(NO3)2•6H2O, and Ti(OC4H9)4 in a molar ratio of Co:Al:Mg:Ti = 0.90:0.04:0.04:0.02.

[0081] Prepare a precipitant solution containing 4.5 mol / L NaOH and 2 mol / L NH3•H2O;

[0082] At 55℃ and pH=12.0, the mixed solution and the precipitant solution were added to the reactor in parallel flow, while nitrogen gas was introduced for protection. The stirring speed was 450 rpm, and the reaction was carried out for 15 hours.

[0083] After the reaction was completed, the sample was filtered, washed, and dried to obtain a spherical Al, Mg, and Ti co-doped cobalt hydroxide precursor.

[0084] Step 2: Lithification treatment

[0085] The precursor and Li2CO3 were mixed at a molar ratio of Li / (Co+Al+Mg+Ti)=1.03:1, heated to 950℃ at 6℃ / min in an oxygen atmosphere, held at that temperature for 15 hours, and then cooled in the furnace.

[0086] Crushing and sieving yielded lithiation products. .

[0087] Step 3: Surface fluorination treatment

[0088] The lithiation product was mixed with AlF3 at a mass ratio of 100:2.5, heated to 750°C at 4°C / min in an argon atmosphere, held at that temperature for 8 hours, and then cooled with the furnace.

[0089] Crushing and sieving yields surface fluorinated products. This process creates an increasing concentration gradient of F element in the shell from the inside out, while simultaneously promoting the migration of Al, Mg, and Ti elements towards the core, creating a decreasing gradient.

[0090] Step 4: Defect Structure Control

[0091] The fluorinated product was heated to 450°C in air at a rate of 3°C / min and held for 5 hours, then cooled in the furnace. The product was then sieved to obtain the final product. This low-temperature annealing treatment induced the removal of oxygen from the surface lattice, forming oxygen vacancy defects with a depth of 5 nm. At the same time, it promoted the migration of Al, Mg, and Ti elements into the oxygen vacancy and uniformly dispersed them.

[0092] Comparative Example 1 (Unmodified LiCoO2)

[0093] Preparation process: Pure Co(OH)2 precursor and Li2CO3 are mixed at Li / Co=1:1 and sintered at 900℃ in an oxygen atmosphere for 12h.

[0094] Comparative Example 2 (Single-element Al doping)

[0095] Composition: LiCo 0.97 Al 0.03 O2

[0096] Preparation process: Same as in Example 1, but only Al source is added, without Mg, Ti and F elements.

[0097] Comparative Example 3 (Coreless / Shell-less Structure)

[0098] Composition: Li 1.05 Co 0.94 Al 0.03 Mg 0.03 O 1.98 F 0.02 (Same as Example 1)

[0099] Preparation process: All raw materials are mixed and sintered in one step, without stepwise fluorination treatment.

[0100] Comparative Example 4 (Defect-free structure)

[0101] Composition: Li 1.01 Co 0.92 Al 0.03 Mg 0.03 Ti 0.02 O 1.99 F 0.01 (Same as Example 2)

[0102] Preparation process: Low-temperature annealing step omitted.

[0103] Comparative Example 5 (three-element doping but disordered distribution)

[0104] Composition: Li 1.03 Co 0.90 Al 0.04 Mg 0.04 Ti 0.02 O 1.96 F 0.04 (Same as Example 3)

[0105] Preparation process: All elemental precursors are directly mixed and sintered, with no gradient fluorination.

[0106] Comparative Example 6

[0107] Material composition: (Same as Example 1), but the F element is uniformly distributed (without gradient) and the M element (Al, Mg) is uniformly distributed (without gradient) in the shell, with no nanoscale oxygen vacancy defects.

[0108] Preparation method: The gradient control step in the surface fluorination treatment is omitted (direct mixing and one-time sintering), and the low-temperature annealing treatment for defect structure control is not performed.

[0109] Comparative Example 7

[0110] Material composition: The amount of M elements (Al, Mg) in the shell decreases by 45% from the inside out (consistent with the M gradient in Example 1), but there is no fluorine element and no nanoscale oxygen vacancy defects.

[0111] Preparation method: The surface fluorination treatment step is eliminated, and only the precursor preparation and lithiation treatment are retained, and low-temperature annealing treatment is not performed.

[0112] Comparative Example 8 (no gradient design, containing only oxygen vacancy defects)

[0113] Material composition: (Same as Example 1), but F and M elements are uniformly distributed (without gradient), and only oxygen vacancy defects with a depth of 20 nm are retained.

[0114] Preparation method: The surface fluorination treatment adopts a uniform mixing and sintering process, and a low-temperature annealing step to retain the defect structure control.

[0115] Comparative Example 9

[0116] Material composition: (Excluding M element), the F element in the shell increases by 2 times from the inside out (only a single fluorine gradient, consistent with the fluorine gradient in the comparative document), with no M element and no nanoscale oxygen vacancy defects.

[0117] Preparation method: The fluoride ion gradient doping method in the prior art is followed (only fluoride salt is mixed with lithium cobalt oxide and then calcined, without M element doping and defect control).

[0118] Experiment 1

[0119] To verify the performance of the present invention, performance tests were conducted on the products of Examples 1-3 and Comparative Examples 1-5, specifically as follows:

[0120] Specific capacity and cycle performance testing: The high-voltage lithium cobalt oxide cathode material of this invention was mixed with a conductive agent (acetylene black) and a binder (polyvinylidene fluoride) at a mass ratio of 8:1:1. N-methylpyrrolidone was added to form a slurry, which was then coated onto aluminum foil and dried to form a cathode sheet. Using lithium metal as the counter electrode, Celgard 2400 as the separator, and a 1 mol / L LiPF6 solution of ethylene carbonate / dimethyl carbonate (volume ratio 1:1) as the electrolyte, a CR2032 coin cell was assembled in an argon-protected glove box. A battery testing system was used to perform charge-discharge cycle tests at a cutoff voltage of 4.5V and above and a charge-discharge rate of 1C. The initial discharge specific capacity and the capacity retention rate after 1000 cycles were recorded.

[0121] Interfacial impedance testing: Using the assembled coin cells described above, AC impedance testing was performed using an electrochemical workstation. The test frequency range was 10 Hz. -2 -10 5 The Hz frequency and the amplitude of 5mV were measured before and after different number of cycles to calculate the rate of increase of the interfacial impedance.

[0122] Lithium-ion diffusion coefficient test: Using the same coin cell as above, cyclic voltammetry tests were performed using an electrochemical workstation at scan rates of 0.1, 0.2, 0.3, 0.4, and 0.5 mV / s. The lithium-ion diffusion coefficient was calculated according to the Randles-Sevcik equation.

[0123] Thermal stability test: A certain amount of the cathode material of this invention was taken and heated from room temperature to 600°C in a thermogravimetric-differential scanning calorimeter filled with argon gas at a heating rate of 10°C / min, and the thermal decomposition initiation temperature of the material was recorded.

[0124] Table 1 Performance data of the products from Examples 1-3:

[0125]

[0126] Table 2 Performance data of the products of Comparative Examples 1-5:

[0127]

[0128] As can be seen from Tables 1 and 2:

[0129] Comparative Example 2 (single Al doping) showed an approximately 89% improvement in cycle life compared to Comparative Example 1 (unmodified), but it was still significantly lower than Examples 1-3 (127%–130% improvement), indicating that the synergistic effect of Al, Mg, and Ti is superior to single-element doping.

[0130] Comparative Example 3 (without core-shell structure) had a capacity retention rate 8.7 percentage points lower than Example 1 and a thermal decomposition temperature 30°C lower, demonstrating that the core-shell structure effectively inhibited electrolyte erosion and structural collapse.

[0131] Comparative Example 4 (defect-free structure) has a lithium-ion diffusion coefficient that is 39.7% lower than that of Example 2 and an interface impedance growth rate that is 66.7% higher, indicating that the nanodefect structure significantly optimizes the ion transport path and stabilizes the SEI film.

[0132] The cycling performance of Comparative Example 5 (disordered distribution) decreased by 6.8 percentage points compared to Example 3, indicating that the gradient distribution of F elements and the uniformly dispersed M elements are crucial to long-term cycling stability.

[0133] Example 3 exhibits a cycle life 2.3 times that of Example 1 at 4.45V high voltage, with thermal stability improved by over 50%, demonstrating the synergistic effect of multi-dimensional modification. In particular, the Al+Mg+Ti combination complements each other in suppressing cation mixing (Mg), enhancing structural rigidity (Al), and improving electronic conductivity (Ti), while the coupling of the gradient F distribution with the defect structure further delays interfacial side reactions, achieving a breakthrough performance improvement.

[0134] This invention achieves a breakthrough improvement in cycle stability under high voltage through unique chemical composition design and microstructure control. In the multi-element synergistic doping strategy, the combination of elements such as Al, Mg, Ti, and Zr plays a complementary role—Al enhances the rigidity of the layered structure of the material and suppresses lattice collapse under high voltage; Mg effectively reduces cation mixing and reduces structural distortion during lithium-ion insertion / extraction; Ti improves electronic conductivity and optimizes charge transport efficiency. This multi-element doping is not a simple performance additive, but rather forms a synergistic effect of "1+1>2" through the interaction between elements. For example, the combination of Al and Mg can simultaneously reduce structural stress and ion migration barriers, an effect far exceeding that of single-element doping.

[0135] The core-shell structure and gradient fluorine doping design specifically address the challenge of interfacial stability under high voltage. The lithium-rich core ensures high specific capacity, while the composite oxide layer containing doped elements in the outer shell acts as a protective barrier, effectively preventing electrolyte corrosion. The gradual increase in fluorine content from the inside out avoids excessive internal fluorine content from hindering lithium-ion diffusion and creates a stable fluoride layer on the surface, significantly reducing the corrosion of the material by HF generated from electrolyte decomposition. This structural design allows the material to maintain a slow increase in interfacial impedance even at high voltages above 4.5V, significantly delaying performance degradation during cycling.

[0136] The introduction of surface nanoscale defect structures further enhances the overall performance of the material. These defects not only provide more channels for rapid diffusion of lithium ions, improving the rate performance of the battery, but also adsorb harmful byproducts generated by electrolyte decomposition, reducing their damage to the main structure of the material. Compared with traditional defect-free materials, the material of this invention maintains a high lithium-ion diffusion coefficient even after long-term cycling, ensuring stable capacity output.

[0137] In practical applications, the advantages of this invention are even more pronounced. First, the high capacity under high voltage is stably maintained. At a cutoff voltage of 4.5V, the specific capacity of the material can reach over 200mAh / g, and the capacity retention rate after 1000 cycles at 1C still exceeds 85%, far surpassing the performance of traditional lithium cobalt oxide materials under the same conditions. This means that lithium-ion batteries using this material can maintain high energy density over a longer service life, meeting the stringent requirements for range in consumer electronics and electric vehicles. Second, the thermal stability of the material is significantly improved, with the thermal decomposition initiation temperature increased by more than 50°C, reducing the risk of thermal runaway in high-temperature environments and providing a more reliable guarantee for the safe use of the battery. In addition, the preparation method is controllable. Through stepwise precursor preparation, lithiation treatment, surface fluorination, and defect control, materials with consistent performance can be stably produced, making it suitable for large-scale industrial production, helping to reduce production costs and promoting its widespread application in actual products.

[0138] In summary, this invention comprehensively addresses the shortcomings of existing high-voltage lithium cobalt oxide materials in terms of cycle stability, interface compatibility, and thermal safety through a combined design of multi-element synergistic doping, core-shell structure, gradient fluorine distribution, and surface defect control, providing crucial material support for the development of high-energy-density lithium-ion batteries.

[0139] Experiment 2

[0140] Electrochemical performance testing: Cyclic stability at 4.6V (vsLi) + / Li), cycled 200 times at 0.5C, and the capacity retention was tested. The test results are as follows:

[0141] Example 1: Capacity retention ≥85% (dual gradient + oxygen vacancy synergistic inhibition of cobalt dissolution and electrolyte decomposition);

[0142] Comparative Example 6 (single fluorine gradient): capacity retention ≤65% (no M gradient to relieve stress, cracking during cycling).

[0143] Comparative Example 9 (Comparative File Migration Scheme): Capacity retention rate ≤50% (no M element to inhibit cobalt dissolution, severe dissolution of transition metals).

[0144] Rate performance: Discharge specific capacity (percentage relative to 0.1C) tested at 1C, 5C, and 10C rates:

[0145] Example 1: 10C capacity retention ≥70% (oxygen vacancies provide rapid Li⁺ diffusion channels);

[0146] Comparative Example 8 (Oxygen vacancies only): 10C capacity retention ≤50% (fluorine-free gradient enhances surface ion conduction, high interfacial impedance).

[0147] Comparative Example 7 (M gradient only): 10C capacity retention ≤45% (no fluorine and oxygen vacancies, poor ion conductivity).

[0148] Interface impedance (EIS): Charge transfer resistance (Rct) before and after test cycles:

[0149] Example 1: Rct growth after cycling ≤30% (M element pinning defect, suppressing impedance rise);

[0150] Comparative Example 6: Rct increases by ≥150% after loop (no gradient of M element, poor interface stability).

[0151] 3. Thermal safety test

[0152] Differential scanning calorimetry (DSC): Tests the peak exothermic temperature and heat release after the material is mixed with the electrolyte.

[0153] Example 1: Exothermic peak temperature ≥220℃, exothermic heat ≤80J / g (fluorine gradient enhances surface oxygen stability and inhibits thermal runaway);

[0154] Comparative Example 9 (Comparative Document Migration Scheme): Exothermic peak temperature ≤180℃, exothermic heat ≥150J / g (no M element, surface oxygen easily desorbed and reacts with electrolyte).

[0155] Conclusion: Due to the synergistic effect of the fluorine gradient increase / M gradient decrease / oxygen vacancy defects, the example significantly outperforms the comparative example in high-pressure cycling stability, rate performance, and thermal safety, demonstrating the synergistic effect of the dual gradient and defect structure. Comparative example 9, lacking the M element and oxygen vacancy design, cannot solve the problems of cobalt dissolution and interfacial impedance under high pressure on lithium cobalt oxide.

[0156] The cathode material of this invention achieves multiple performance enhancements through a dual-gradient design: the F element content gradually increases from the inside out, while the M element concentration gradually decreases from the inside out. This, combined with the nanoscale oxygen vacancy defect structure and the uniform dispersion of M element within the defects, results in the increased F element content in the outer shell by 1.5-3 times from the inside out, strengthens surface oxygen stability and effectively inhibits electrolyte decomposition. The decreased M element content by 30%-60% from the inside out alleviates core-shell interface stress, inhibits cracking during cycling, and simultaneously reduces the outer shell modulus to absorb volumetric strain during charge and discharge. The nanoscale oxygen vacancy defects are Li... + Diffusion provides a rapid pathway, while the uniform dispersion of M element at defects acts as a pinning agent, reducing interfacial impedance. These synergistic effects enable breakthroughs in key indicators such as cycle stability, rate performance, and thermal safety of the material under 4.6V high voltage conditions. It can effectively suppress cobalt dissolution under high voltage and solve the multi-dimensional failure problem in high-voltage lithium cobalt oxide applications.

[0157] It is worth noting that by preparing precursors containing M element through co-precipitation, followed by lithiation, surface fluorination, and defect structure modulation, the core-shell structure, dual gradient distribution, and nanoscale oxygen vacancy defects of the material can be precisely achieved. Specifically, the second high-temperature sintering temperature is lower than the first, ensuring the gradient distribution of fluorine; the low-temperature annealing treatment is carried out in an oxygen-containing atmosphere, which effectively induces oxygen vacancy formation and promotes the migration and dispersion of M element, resulting in strong process controllability.

[0158] The above specific embodiments are merely several optional embodiments of the present invention. Based on the technical solutions of the present invention and the relevant teachings of the above embodiments, those skilled in the art can make various alternative improvements and combinations to the above specific embodiments.

Claims

1. A high-voltage lithium cobalt oxide cathode material, characterized in that, The chemical composition of the cathode material is as follows: ,in It consists of at least two elements selected from Al, Mg, Ti, and Zr. , , ; The cathode material has a core-shell structure, with the core being a lithium-rich lithium cobalt oxide phase and the outer shell being a lithium-containing... Composite oxide layers of elements; The outer shell The content of elements gradually increases from the inside out, and The concentration of the element in the shell gradually decreases from the inside to the outside; the shell The elemental content increases 1.5-3 times from the inner layer to the outer layer. The element content decreases by 30%-60% from the inner layer to the outer layer; The primary particle surface of the cathode material has a nanoscale oxygen vacancy defect structure, in which uniformly dispersed oxygen vacancy defects are distributed. The element, and the depth of the oxygen vacancy defect is 5-50 nm.

2. The high-voltage lithium cobalt oxide cathode material according to claim 1, characterized in that, The The elements are a combination of Al and Mg, where the molar content of Al is... The molar content of Mg is ,and .

3. The high-voltage lithium cobalt oxide cathode material according to claim 1, characterized in that, The The elements are a combination of Al, Mg, and Ti, with the molar content of Al being [missing information]. The molar content of Mg is The molar content of Ti is ,and .

4. The high-voltage lithium cobalt oxide cathode material according to claim 1, characterized in that, In the core-shell structure, the core occupies 70% to 90% of the total particle volume, and the outer shell has a thickness of 50-200 nm.

5. The high-voltage lithium cobalt oxide cathode material according to claim 1, characterized in that, The specific surface area of ​​the positive electrode material is 0.2-0.8 m². 2 / g, tap density is 2.8-3.4g / cm³ 3 .

6. A method for preparing a high-voltage lithium cobalt oxide cathode material as described in any one of claims 1-5, characterized in that, Includes the following steps: Preparation of precursors: cobalt salt, Salts of the element are prepared into a mixed solution according to stoichiometric ratio, and a precipitating agent is added to carry out a coprecipitation reaction to obtain a solution containing... Cobalt hydroxide precursor of element; Lithification process: The precursor is mixed with a lithium source and subjected to a first high-temperature sintering in an oxygen atmosphere to obtain the lithiation product; Surface fluorination treatment: The lithium product is mixed with a fluorine source and subjected to a second high-temperature sintering in an inert atmosphere. The temperature of the second high-temperature sintering is lower than that of the first high-temperature sintering. Defect structure manipulation: The surface-fluorinated product is subjected to low-temperature annealing in an oxygen-containing atmosphere to form the nanoscale defect structure. This low-temperature annealing, performed in an oxygen-containing atmosphere, induces the release of oxygen from the surface lattice, forming oxygen vacancy defects, and simultaneously promotes… Elements migrate into oxygen vacancies and disperse uniformly.

7. The method for preparing a high-voltage lithium cobalt oxide cathode material according to claim 6, characterized in that, The first high-temperature sintering is performed at a temperature of 850-950℃ for 8-15 hours; the second high-temperature sintering is performed at a temperature of 600-750℃ for 4-8 hours; and the low-temperature annealing is performed at a temperature of 300-500℃ for 2-6 hours.

8. The method for preparing a high-voltage lithium cobalt oxide cathode material according to claim 6, characterized in that, The fluorine source is , , At least one of them, and the amount of fluorine source added is 0.5% to 3% of the mass of the lithiation product.

9. The method for preparing a high-voltage lithium cobalt oxide cathode material according to claim 6, characterized in that, The lithium source is at least one of lithium carbonate and lithium hydroxide, and the molar ratio of the lithium source to the metal element in the precursor is 1.01:1 to 1.05:

1.

10. The method for preparing a high-voltage lithium cobalt oxide cathode material according to claim 6, characterized in that, The precipitant is a mixed solution of sodium hydroxide and ammonia. The pH value of the coprecipitation reaction is controlled at 10.5-12.0, and the reaction temperature is 40-60℃.

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