A lithium nickel manganese cobalt oxide material with high cycle stability and a warm isostatic pressing preparation method thereof

Abstract

This application relates to the field of lithium battery technology, and provides a lithium nickel manganese cobalt oxide material with high cycle stability and a method for preparing the material by warm isostatic pressing. The method includes the following steps: S100, mixing an organic precursor with lithium nickel manganese cobalt oxide powder to obtain a mixture; S200, subjecting the mixture to warm isostatic pressing to form a carbon coating layer, followed by cooling and depressurization to obtain the lithium nickel manganese cobalt oxide material. This application utilizes warm isostatic pressing technology to simultaneously carbonize the organic precursor and construct a dense and uniform carbon coating layer on the surface of the lithium nickel manganese cobalt oxide particles. This layer structure significantly improves interparticle contact, enhances the bulk conductivity of the material, and strengthens the electrode-electrolyte interface stability, thereby reducing interfacial impedance and improving cycle life and rate performance.

Description

Technical Field

[0001] This application relates to the field of lithium battery technology, and in particular to a lithium nickel manganese cobalt oxide material with high cycle stability and a method for preparing the material by warm isostatic pressing. Background Technology

[0002] Lithium-ion batteries, with their high energy density, good power performance, and high cycle efficiency, have become the core electrochemical energy storage technology for portable electronics, power batteries, and energy storage systems. Among many cathode materials, lithium nickel manganese cobalt oxide (LiNi) is a popular choice. x Mn y Co z O2 (NMC) is widely used in medium-to-high energy density battery systems due to its high specific capacity and good overall performance.

[0003] However, NMC materials, especially those with high nickel content, suffer from insufficient interfacial stability during long-term cycling. Their surfaces are prone to side reactions with air or electrolyte, leading to increased interfacial impedance, accelerated loss of active lithium, and consequently, capacity decay and reduced cycling performance. To improve interfacial properties, existing research commonly employs carbon coating strategies. However, traditional carbon coating methods often struggle to form a complete, dense, and uniformly thick carbon layer on the particle surface, resulting in unsatisfactory coating effects. Problems such as uneven coating, uncovered areas, or excessively thick carbon layers hindering lithium-ion transport arise, limiting the full realization of their modification effects.

[0004] Therefore, there is an urgent need for a new preparation technology and process route that can achieve the construction of a dense and uniform carbon coating layer on the surface of NMC particles while taking into account the stability of the material phase structure. Summary of the Invention

[0005] In view of the above-mentioned shortcomings in the prior art, the purpose of this application is to provide a lithium nickel manganese cobalt oxide material with high cycle stability and a method for preparing the material by warm isostatic pressing.

[0006] To achieve the above-mentioned objectives, the technical solution adopted in this application is as follows: By using the warm isostatic pressing technique, a dense and uniform carbon coating layer is constructed on the surface of lithium nickel manganese cobalt oxide particles while carbonizing the organic precursor. This layer structure can significantly improve the contact between particles, enhance the bulk conductivity of the material, and strengthen the stability of the electrode-electrolyte interface, thereby reducing the interface impedance and improving cycle life and rate performance.

[0007] In a first aspect, embodiments of this application provide a method for preparing lithium nickel manganese cobalt oxide materials with high cycle stability by warm isostatic pressing, comprising the following steps: S100, mixing an organic precursor with lithium nickel manganese cobalt oxide powder to obtain a mixture; S200, subjecting the mixture to warm isostatic pressing to form a carbon coating layer, and obtaining the lithium nickel manganese cobalt oxide material after cooling and depressurization treatment.

[0008] In an optional embodiment, in step S100, the organic precursor includes at least one of sucrose, polyvinyl alcohol, methylcellulose, or acrylic oligomers; and / or the mass ratio of the organic precursor to the lithium nickel manganese cobalt oxide powder is (0.1-8):100; and / or the mixing process includes at least one of wet stirring, spray drying or dry mixing, and ball milling; wherein, wet stirring uses deionized water or a low-volatility solvent as the dispersion medium.

[0009] In an optional embodiment, before step S100, the method further includes: S001, drying the lithium nickel manganese cobalt oxide powder to make the moisture content of the lithium nickel manganese cobalt oxide powder 0.1-0.5wt%.

[0010] In an optional embodiment, in step S100, the organic precursor further includes a functional additive; wherein the functional additive includes at least one of a phosphorus-containing precursor, an aluminum-containing precursor, a boron-containing precursor, or a metal-organic complex, and the amount of the functional additive is 0.01-2.0 wt%.

[0011] In an optional embodiment, in step S200, the mixture is filled into an inner liner with a filling density of 40-70%, and the inner liner includes at least one of a metal inner mold, a graphite inner mold, or a can-in-can structure.

[0012] In an optional implementation, in step S200, the warm isostatic pressing (WIP) treatment is carried out in an inert atmosphere, and the WIP treatment includes a first stage and a second stage; the pressure of the first stage is 10-50 MPa, the temperature is 300-420°C, and the time is 1-5 min; the pressure of the second stage is 50-200 MPa, the temperature is 350-450°C, and the time is 10-60 min.

[0013] In an optional embodiment, in step S200, the cooling treatment and the depressurization treatment are carried out in an inert atmosphere; the cooling treatment includes cooling to room temperature at a cooling rate of 3-8°C / min; the depressurization treatment includes performing a first depressurization at a rate of 5-20 MPa / min, followed by a second depressurization at a rate of 0.5-5 MPa / min, until the pressure drops to atmospheric pressure.

[0014] In an optional embodiment, after step S200, the method further includes: S300, performing a post-annealing treatment on the lithium nickel manganese cobalt oxide material at 200-300°C for 30-180 minutes under an inert atmosphere.

[0015] Secondly, embodiments of this application provide a lithium nickel manganese cobalt oxide material, prepared by any of the above-described processing methods. The lithium nickel manganese cobalt oxide material includes active particles and a carbon coating layer covering at least a portion of the surface of the active particles; wherein the chemical formula of the lithium nickel manganese cobalt oxide material is LiNi. x Mn y Co z O2, and 0 <x<1、0<y<1、0<z<1,x+y+z=1。

[0016] In one alternative embodiment, the active particles have a D50 of 5-15 μm and a carbon coating thickness of 0.5-50 nm.

[0017] The beneficial effects of this application include at least the following: (1) A dense and uniform carbon coating layer was constructed on the surface of NMC particles by means of warm isostatic pressing technology, which solved the problem of unevenness and incompleteness of traditional coating methods.

[0018] (2) The carbon coating layer of this application is firmly bonded to the particles, which can significantly improve the physical and electrical contact between active particles, construct an efficient electronic conductive network, thereby greatly improving the bulk electronic conductivity of the material; at the same time, the coating layer, as a stable physical barrier, can effectively block the direct erosion of the surface of the active material by the electrolyte, significantly enhance the chemical stability of the electrode-electrolyte interface, and reduce the occurrence of side reactions. Detailed Implementation

[0019] To make the technical problems, technical solutions, and beneficial effects to be solved by this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are only for explaining this application, but the implementation of this application is not limited thereto.

[0020] Unless otherwise defined, the technical terms used in the following embodiments have the same meanings as commonly understood by those skilled in the art to which this application pertains. Unless otherwise specified, the experimental reagents used in the following embodiments are conventional biochemical reagents; the amounts of experimental reagents used are, unless otherwise specified, the amounts used in conventional experimental operations; and the experimental methods used are, unless otherwise specified, conventional methods.

[0021] Lithium-ion batteries, as efficient and clean energy storage carriers, have been widely used in electric vehicles and large-scale energy storage. Their performance is highly dependent on cathode materials, among which NMC has attracted much attention due to its high specific capacity and cost advantages. However, NMC materials, especially those with high nickel content, have an inherent defect of insufficient interfacial stability, which easily leads to capacity decay during long-term cycling. Existing carbon coating improvement technologies are difficult to form a uniform and dense carbon layer on the particle surface, often resulting in incomplete coating or uneven thickness, which in turn restricts the full realization of their electrochemical performance.

[0022] In a first aspect, embodiments of this application provide a method for preparing lithium nickel manganese cobalt oxide materials with high cycle stability by warm isostatic pressing, comprising the following steps: S100. The organic precursor is mixed with lithium nickel manganese cobalt oxide powder to obtain a mixture; S200. The mixture is subjected to warm isostatic pressing to form a carbon coating layer. After cooling and depressurization, lithium nickel manganese cobalt oxide material is obtained.

[0023] Preferably, in step S100, thoroughly mixing the organic precursor with the NMC powder is a prerequisite for constructing a uniform carbon coating layer. The organic precursor includes at least one of sucrose, polyvinyl alcohol, methylcellulose, or acrylic oligomers. These materials can be carbonized at high temperatures to form amorphous carbon with good conductivity. By controlling the mass ratio of the organic precursor to the NMC powder to be (0.1-8):100, the thickness of the final carbon coating layer can be controlled, ensuring the formation of a complete conductive network while avoiding an excessively thick carbon layer that hinders lithium ion insertion / extraction. The mixing process includes at least one of wet stirring, spray drying or dry mixing, and ball milling. Wet stirring uses deionized water or a low-volatility solvent as the dispersion medium. Mechanical force or solvent dispersion ensures that the organic precursor is uniformly attached to the surface of each NMC particle at the molecular or nanoscale, laying a solid foundation for the subsequent formation of a continuous and dense coating layer during isostatic pressing.

[0024] Furthermore, prior to step S100, the process includes: S001, drying the lithium nickel manganese cobalt oxide powder to reduce its moisture content to 0.1-0.5 wt%. This drying process eliminates the adverse effects of residual moisture on the subsequent carbon coating process and the final material properties.

[0025] Specifically, if the moisture content of lithium nickel manganese cobalt oxide powder is too high, the surface adsorbed water will rapidly vaporize and generate water vapor during the subsequent isostatic pressing stage. This water vapor creates localized high pressure at the confined particle-carbon layer interface, easily leading to defects such as blistering, swelling, or even localized detachment of the coating layer. Pre-drying can significantly reduce the formation of such interfacial gas byproducts, thus laying the foundation for the formation of a complete and dense carbon coating layer. Simultaneously, pre-drying treatment can effectively improve the wettability and spreading uniformity of organic precursors on the powder particle surface. The presence of moisture alters the powder surface energy, potentially hindering the uniform adsorption of organic matter; after moisture removal, organic precursors are more likely to form continuous and uniform films, which are then transformed into a denser carbon layer with lower porosity and better conductivity during subsequent carbonization. From a chemical stability perspective, residual moisture reacts with active lithium compounds under high temperature and pressure, generating electrochemically inert byproducts such as LiOH and Li₂CO₃, which not only consume active lithium and reduce capacity but also increase interfacial impedance. Pre-drying can suppress such side reactions to the greatest extent, ensuring the chemical purity and electrochemical activity of the electrode material.

[0026] In addition, controlling the moisture content within the range of 0.1-0.5wt% can not only fully remove harmful free water and most of the adsorbed water, avoiding their negative impact on the process and performance, but also prevent the powder from developing microcracks or structural damage due to excessive dehydration, thus ensuring the robustness of subsequent processing and the overall performance of the final product.

[0027] Furthermore, in step S100, the organic precursor also includes functional additives; wherein the functional additives include at least one of phosphorus-containing precursors, aluminum-containing precursors, boron-containing precursors, or organometallic complexes, and the amount of functional additives added is 0.01-2.0 wt%; so that during the carbon coating process, the functional additives can participate in the reaction simultaneously and synergistically construct a composite surface layer with enhanced structural stability and interfacial chemical stability, thereby further improving the overall electrochemical performance of the material.

[0028] Specifically, phosphorus-containing precursors can react with metals or lithium ions on the material surface during carbonization or post-annealing to form a thin layer of metal phosphates or phosphate esters. This layer acts as a stable passivation film in the electrolyte, effectively suppressing interfacial side reactions and reducing charge transfer impedance. Aluminum-containing precursors can form an extremely thin Al2O3 coating layer or aluminum-doped region at high temperatures, acting as a structural passivation layer, reducing crystal surface reconstruction, and suppressing lithium-transition metal ion mixing, thereby improving the structural stability and cycle life of the material. Boron-containing precursors can form a BO network structure or be incorporated into a carbon layer, not only enhancing the bonding force between the carbon layer and the matrix but also improving the chemical stability of the carbon layer in the electrolyte and contributing to the continuity of the surface conductive network. Organometallic complexes decompose during carbonization, forming micro- or nano-scale metal or oxide dispersions in situ on the material surface. These dispersions can act as conductive bridges to enhance electron conduction and catalyze the conversion of organic components to partially graphitized carbon, further improving overall electronic conductivity.

[0029] In addition, by controlling the amount of functional additives to 0.01-2.0 wt%, the interfacial chemical and mechanical stability can be improved without destroying the bulk stoichiometry and lattice of NMC, thereby improving cycle and rate performance.

[0030] Preferably, in step S200, warm isostatic pressing is employed, simultaneously applying high temperature and uniform isostatic pressure in an inert atmosphere to achieve the synergistic process of in-situ carbonization of the organic precursor and densification of the particle structure. On the one hand, this promotes the gradual formation of a carbon-rich amorphous phase during decomposition, dehydrogenation, and decarboxylation reactions of the organic matter, and partial graphitization under appropriate conditions. On the other hand, the high-pressure environment facilitates the tight coating of the carbon layer onto the particle surface, significantly reducing interfacial porosity and forming a continuous and dense carbon coating layer. Simultaneously, isostatic pressing promotes the movement of micro-dislocations between particles, surface reconstruction, and contact bonding, effectively compressing internal pores and interfacial gaps, thereby reducing electron and ion transport impedance and improving the bulk conductivity and mechanical integrity of the material.

[0031] Furthermore, the warm isostatic pressing (WIP) process is carried out in an inert atmosphere and includes a first stage and a second stage. The first stage involves a pressure of 10-50 MPa, a temperature of 300-420°C, and a time of 1-5 min. The second stage involves a pressure of 50-200 MPa, a temperature of 350-450°C, and a time of 10-60 min. The first stage, conducted at a lower temperature and moderate pressure, allows the organic precursor to soften, melt, decompose, and undergo preliminary carbonization, enabling the organic matter to fully decompose and release small volatile molecules, preventing excessive gas production due to rapid decomposition that could lead to porous or cracked coating layers. The second stage, conducted at a higher pressure and moderate temperature, further optimizes the densification and carbon layer structure, promoting synergistic sintering and bonding between particles and the carbon layer to obtain a low-resistance and mechanically stable composite particle structure. At high temperatures, carbon materials possess a certain degree of plasticity, and the extremely high isotropic pressure allows them to flow and fill all microscopic voids, ultimately achieving complete densification of the carbon layer and minimizing interparticle contact resistance. Thus, warm isostatic pressing not only significantly improves the electronic conductivity of materials, but also constructs a firmly bonded and dense carbon coating layer on the particle surface.

[0032] Furthermore, in step S200, the mixture is loaded into an inner liner with a filling density of 40-70%, and the inner liner includes at least one of a metal inner mold, a graphite inner mold, or a can-in-can structure. The inner liner filling density is 40-70%. If the filling density is too low, the powder is prone to excessive displacement during pressurization, leading to decreased densification efficiency and poor coating uniformity. If the filling density is too high, the volatiles released by the thermal decomposition of organic matter will be difficult to discharge smoothly, accumulating inside and forming high pressure, causing the coating layer to rupture or generate structural defects. Regarding the inner liner material, a metal inner mold has excellent thermal conductivity and mechanical strength, which helps to achieve uniform heat conduction and pressure transmission; a graphite inner mold has good thermal stability and chemical inertness, and can maintain interface cleanliness under high temperature and high pressure environments; while the can-in-can structure, through its double-layer container design, further isolates the material from the external environment, effectively preventing contamination and enabling independent control of local atmosphere or pressure gradients, thereby optimizing the reliability and consistency of the overall process.

[0033] Furthermore, the cooling and decompression treatments are conducted in an inert atmosphere. The cooling process includes cooling to room temperature at a rate of 3-8°C / min; the decompression treatment includes a first decompression at a rate of 5-20 MPa / min, followed by a second decompression at a rate of 0.5-5 MPa / min until atmospheric pressure is reached. During the cooling phase, the slow cooling at a rate of 3-8°C / min helps to equalize the thermal stress caused by the difference in thermal expansion coefficients between the material and the carbon coating, preventing microcracks or interfacial delamination due to rapid cooling, thus maintaining the continuity of the coating and close contact between particles. During the decompression phase, a first decompression is performed at a relatively fast rate to reduce the system pressure to a safe intermediate value, releasing most of the compressible gas; subsequently, a second decompression is performed at a lower rate, allowing sufficient time for residual gas to gradually escape from the material, preventing the formation of voids or localized delamination under the coating due to rapid gas expansion. The entire cooling and decompression process is conducted under an inert atmosphere to prevent oxidation of the carbon layer or functional additives at high temperatures, ensuring the stability of their chemical state and structural function.

[0034] Furthermore, following step S200, the process includes S300: post-annealing the lithium nickel manganese cobalt oxide material at 200-300℃ for 30-180 minutes under an inert atmosphere. This step stabilizes the structure of the carbon coating layer, repairs defects, removes residual organic matter, and improves the carbon-matrix interface contact, thereby enhancing the material's conductivity, interfacial chemical stability, first-cycle coulombic efficiency, and cycle stability. The heat treatment provides the system with adequate energy, promoting the complete decomposition of residual organic matter, the release of adsorbed gases, and the elimination of internal stress accumulated during isostatic pressing, achieving densification and defect repair at the carbon layer-matrix interface. During the low-temperature heat treatment, the carbon layer undergoes localized short-range ordered arrangement, exhibiting a slight graphitization trend, thereby improving electron mobility and the chemical stability of the carbon layer itself. The surface species formed by the functional additives are further uniformly distributed or crystallized during annealing, forming a stable and continuous interfacial protective layer, effectively suppressing electrolyte side reactions and reducing interfacial impedance. Thus, post-annealing treatment optimizes the conductivity, interfacial bonding strength, and overall chemical stability of the carbon coating layer while maintaining the NMC main structure from high-temperature damage, thereby improving the material's first-cycle coulombic efficiency and enhancing its long-cycle performance.

[0035] Secondly, embodiments of this application provide a lithium nickel manganese cobalt oxide material with high cycle stability, prepared by any of the above-described processing methods. The lithium nickel manganese cobalt oxide material includes active particles and a carbon coating layer covering at least a portion of the surface of the active particles; wherein the chemical formula of the lithium nickel manganese cobalt oxide material is LiNi. x Mn y Co zO2, and 0 <x<1、0<y<1、0<z<1,x+y+z=1。

[0036] Preferably, the active particles use lithium nickel manganese cobalt oxide as the base material, and a balance between high capacity, structural stability, and safety is achieved by adjusting the transition metal ratio. Among them, nickel contributes to high specific capacity, manganese helps stabilize the crystal structure, and cobalt improves the material's lithium conductivity and layered structure regularity. This allows the material to maintain good thermal stability and cycle durability while possessing high energy density, laying a chemical foundation for constructing high-performance cathode materials.

[0037] In one optional implementation, the active particles have a D50 of 5-15 μm and a carbon coating thickness of 0.5-50 nm. Controlling the D50 of the active particles within the 5-15 μm range allows for smaller particles, which, while shortening the lithium-ion diffusion length and improving rate capability, also results in a larger specific surface area, exacerbating side reactions with the electrolyte and leading to accelerated cycle decay and increased first-time irreversible losses. Larger particles, on the other hand, reduce the interparticle contact area, hindering electron and ion transport at high rates and reducing the electrode's specific capacity. The thickness of the carbon coating layer is controlled between 0.5-50 nm. When the thickness is greater than 0.5 nm, a conductive film that covers and connects the layers can be formed, which can effectively improve the surface electronic conductivity and block the direct erosion of the active surface by the electrolyte. In the thin layer range of 0.5-10 nm, the carbon layer has very little resistance to the penetration of lithium ions, while providing a significant electron transport pathway and interface passivation effect. As the thickness gradually approaches the upper limit, the protective and conductive network of the carbon layer is further enhanced, but excessive thickness will increase irreversible mass, reduce volumetric energy density, and may increase the diffusion resistance of lithium ions at the interface, thereby reducing the reversible capacity at high rates.

[0038] This application has undergone multiple experiments, and some of the test results are presented here for reference to further describe the invention in detail. The following is a detailed description in conjunction with specific embodiments.

[0039] Example 1 This embodiment provides a lithium nickel manganese cobalt oxide material with high cycle stability and a method for preparing the material by warm isostatic pressing, specifically including the following steps: S001. The lithium nickel manganese cobalt oxide powder is subjected to vacuum drying to reduce its moisture content to 0.2 wt%. S100. Sucrose and lithium nickel manganese cobalt oxide powder are wet-stirred at a mass ratio of 5:100, using deionized water as the dispersion medium, and 1.0 wt% phosphate is added to obtain a mixture. S200. In an argon atmosphere, the mixture is loaded into the inner liner of a metal inner mold, and after vibration compaction to a filling density of 60%, it is subjected to isostatic pressing to form a carbon coating layer. After cooling and decompression treatment, lithium nickel manganese cobalt oxide material is obtained. S300. Under an argon atmosphere, the lithium nickel manganese cobalt oxide material is subjected to a post-annealing treatment at 250°C for 100 minutes to obtain the finished product. The isostatic pressing process consists of two stages: the first stage has a pressure of 30 MPa, a temperature of 350 °C, and a time of 3 min; the second stage has a pressure of 100 MPa, a temperature of 400 °C, and a time of 20 min. The cooling process includes cooling to room temperature at a rate of 5°C / min; the decompression process includes a first decompression at a rate of 10 MPa / min, followed by a second decompression at a rate of 3 MPa / min, until the pressure drops to atmospheric pressure.

[0040] Example 2 This embodiment provides a lithium nickel manganese cobalt oxide material with high cycle stability and a method for preparing the material by warm isostatic pressing, specifically including the following steps: S001. Under an argon atmosphere, lithium nickel manganese cobalt oxide powder is subjected to hot air drying to reduce its moisture content to 0.1 wt%. S100. Polyvinyl alcohol and lithium nickel manganese cobalt oxide powder are dry-mixed at a mass ratio of 0.1:100, and 0.01wt% aluminum nitrate is added to obtain a mixture. S200. In an argon atmosphere, the mixture is loaded into the inner liner of a graphite inner mold, and after vibration compaction to a filling density of 40%, it is subjected to isostatic pressing to form a carbon coating layer. After cooling and decompression treatment, lithium nickel manganese cobalt oxide material is obtained. S300. Under an argon atmosphere, the lithium nickel manganese cobalt oxide material is subjected to a post-annealing treatment at 200°C for 180 minutes to obtain the finished product. The isostatic pressing process consists of two stages: the first stage has a pressure of 10 MPa, a temperature of 300 °C, and a time of 5 min; the second stage has a pressure of 50 MPa, a temperature of 350 °C, and a time of 60 min. The cooling process includes cooling to room temperature at a rate of 3°C / min; the decompression process includes a first decompression at a rate of 5 MPa / min, followed by a second decompression at a rate of 0.5 MPa / min, until the pressure drops to atmospheric pressure.

[0041] Example 3 This embodiment provides a lithium nickel manganese cobalt oxide material with high cycle stability and a method for preparing the material by warm isostatic pressing, specifically including the following steps: S001. Under an argon atmosphere, the lithium nickel manganese cobalt oxide powder is subjected to hot air drying to reduce its moisture content to 0.5 wt%. S100. Methylcellulose and lithium nickel manganese cobalt oxide powder are spray-dried at a mass ratio of 8:100, and 2.0wt% boric acid is added to obtain a mixture. S200. In an argon atmosphere, the mixture is loaded into a can-in-can structured inner liner, and after vibration compaction to a filling density of 70%, it is subjected to isostatic pressing to form a carbon coating layer. After cooling and decompression treatment, lithium nickel manganese cobalt oxide material is obtained. S300. Under an argon atmosphere, the lithium nickel manganese cobalt oxide material is subjected to a post-annealing treatment at 300°C for 30 minutes to obtain the finished product. The isostatic pressing process consists of two stages: the first stage has a pressure of 50 MPa, a temperature of 420°C, and a time of 1 min; the second stage has a pressure of 200 MPa, a temperature of 450°C, and a time of 10 min. The cooling process includes cooling to room temperature at a rate of 8°C / min; the decompression process includes a first decompression at a rate of 20 MPa / min, followed by a second decompression at a rate of 5 MPa / min, until the pressure drops to atmospheric pressure.

[0042] Example 4 This embodiment provides a lithium nickel manganese cobalt oxide material with high cycle stability and a method for preparing the material by warm isostatic pressing, specifically including the following steps: S001. Under an argon atmosphere, lithium nickel manganese cobalt oxide powder is subjected to hot air drying to reduce its moisture content to 0.3 wt%. S100. Methylcellulose and lithium nickel manganese cobalt oxide powder were spray-dried at a mass ratio of 6:100, and 1.2wt% Ti(OiPr)4 was added to obtain a mixture. S200. In an argon atmosphere, the mixture is loaded into a can-in-can structured inner liner, and after vibration compaction to a filling density of 60%, it is subjected to isostatic pressing to form a carbon coating layer. After cooling and decompression treatment, lithium nickel manganese cobalt oxide material is obtained. S300. Under an argon atmosphere, the lithium nickel manganese cobalt oxide material is subjected to a post-annealing treatment at 280°C for 50 minutes to obtain the finished product. The isostatic pressing process consists of two stages: the first stage has a pressure of 40 MPa, a temperature of 320°C, and a time of 2 min; the second stage has a pressure of 150 MPa, a temperature of 400°C, and a time of 10 min. The cooling process includes cooling to room temperature at a rate of 6°C / min; the decompression process includes a first decompression at a rate of 12 MPa / min, followed by a second decompression at a rate of 2 MPa / min, until the pressure drops to atmospheric pressure.

[0043] Example 5 This embodiment provides a warm isostatic pressing method for preparing lithium nickel manganese cobalt oxide materials with high cycle stability. The lithium nickel manganese cobalt oxide material and preparation method are the same as those shown in Embodiment 1, except that post-annealing treatment is not performed, i.e., step S300 is omitted.

[0044] Example 6 This embodiment provides a method for preparing lithium nickel manganese cobalt oxide material with high cycle stability by warm isostatic pressing. The lithium nickel manganese cobalt oxide material and preparation method are the same as those in Embodiment 1, except that no functional additives are added in step S100.

[0045] Comparative Example 1 This comparative example provides a method for preparing lithium nickel manganese cobalt oxide material with high cycle stability by warm isostatic pressing. The lithium nickel manganese cobalt oxide material and preparation method are the same as those shown in Example 1, except that there is no carbon coating layer, that is, no organic precursor is added in step S100.

[0046] Comparative Example 2 This comparative example provides a warm isostatic pressing method for preparing lithium nickel manganese cobalt oxide materials with high cycle stability. The lithium nickel manganese cobalt oxide material and preparation method are the same as those shown in Example 1, except that in step S200, conventional liquid-phase mixing followed by atmospheric pressure sintering is used for carbon coating, instead of warm isostatic pressing.

[0047] Test method: The lithium nickel manganese cobalt oxide materials prepared in Examples 1-6 and Comparative Examples 1-2 were subjected to the following tests, and the test results are shown in Table 1: Particle size distribution of active particles: According to the national standard GB / T 19077-2016 "Particle size distribution by laser diffraction", the sample powder was ultrasonically dispersed in anhydrous ethanol and then measured using a laser particle size analyzer.

[0048] Carbon coating thickness: Measured using high-resolution transmission electron microscopy. After ultrasonically dispersing the sample powder in ethanol, the suspension was dropped onto a copper grid with a carbon support film. After drying, it was observed under HR-TEM to directly measure the thickness of the amorphous carbon layer on the particle edge surface.

[0049] Tap density: The tap density was determined according to the method specified in the national standard GB / T 5162-2021 "Determination of tap density of metal powder".

[0050] Table 1 The active materials prepared in Examples 1-6 and Comparative Examples 1-2 were used as positive electrode active materials, and mixed with conductive agent acetylene black and binder in a mass ratio of 92:4:4. The mixture was then uniformly coated onto an aluminum foil current collector, vacuum dried, rolled, and punched into positive electrode sheets. In an argon-filled glove box, a CR2032 type button cell was assembled using a lithium metal sheet as the counter / reference electrode, a polypropylene microporous membrane as the separator, and a 1 mol / L LiPF6 solution of ethylene carbonate / diethyl carbonate as the electrolyte.

[0051] Powder conductivity: Referring to the test method of powder resistivity in GB / T 30835-2014 "Carbon Composite Lithium Iron Phosphate Cathode Material for Lithium-ion Batteries", the four-probe method was used. The sample powder was pressed into a disc under constant pressure and then measured and the conductivity was calculated.

[0052] Initial discharge specific capacity and coulombic efficiency: After assembly, the battery was left to stand for 12 hours and then tested using a battery testing system such as Blue Electric at 25±2℃. The charge / discharge regime was as follows: constant current charging at 0.1C to 4.3V, followed by constant voltage charging until the current dropped to 0.05C; after standing for 5 minutes, constant current discharging at 0.1C to 3.0V. The calculation formula is as follows: Initial discharge specific capacity (mAh / g) = (discharge current × discharge time) / mass of active material Initial coulombic efficiency (%) = (Initial discharge capacity / Initial charge capacity) × 100% Capacity retention: After the initial charge-discharge test, the battery underwent continuous constant-current charge-discharge cycle testing at a 1C rate. The upper limit of the cycle voltage was 4.3V, and the lower limit was 3.0V. The calculation formula is as follows: Capacity retention rate (%) = (Discharge capacity at the 500th discharge / Discharge capacity at the 1st discharge) × 100% Interfacial impedance: Electrochemical impedance spectroscopy (EIS) was performed on the battery after cycle testing using an electrochemical workstation. The test was conducted at the battery's open-circuit voltage, with a frequency range of 100 kHz to 10 mHz and a perturbation signal amplitude of 5 mV.

[0053] Table 2 As shown in Tables 1 and 2, compared with Comparative Example 1, Example 1 exhibits a significantly improved carbon coating layer, with its powder conductivity increased by four orders of magnitude. The interfacial impedance after cycling is significantly reduced, and the capacity retention is high, demonstrating that the carbon coating layer is crucial for constructing a conductive network, reducing impedance, and stabilizing the interface. Compared with Comparative Example 2, the carbon coating layer of Example 1 is more uniform and dense, resulting in higher tap density, conductivity, and superior cycling performance, demonstrating the unique advantages of warm isostatic pressing technology in achieving uniform coating and particle densification.

[0054] Example 5, without post-annealing, exhibited slightly worse cycling performance than Example 1 and higher impedance, indicating that post-annealing helps eliminate stress and stabilize the material structure. Example 6, without functional additives, showed slightly lower cycling performance than Example 1, indicating that additives can further strengthen the interface and improve long-term cycling stability.

[0055] In summary, the test data above demonstrate that the warm isostatic pressing method of this application can successfully construct a uniform carbon coating layer, significantly improving the conductivity, tap density and interfacial stability of the material, thereby ultimately achieving high cycle stability and rate performance.

[0056] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application, and should all be included within the protection scope of this application.

Claims

1. A method for preparing lithium nickel manganese cobalt oxide materials with high cycle stability by warm isostatic pressing, characterized in that, The preparation method includes the following steps: S100. The organic precursor is mixed with lithium nickel manganese cobalt oxide powder to obtain a mixture; S200. The mixture is subjected to warm isostatic pressing to form a carbon coating layer. After cooling and decompression treatment, the lithium nickel manganese cobalt oxide material is obtained.

2. The preparation method according to claim 1, characterized in that, In step S100, The organic precursor includes at least one of sucrose, polyvinyl alcohol, methylcellulose, or acrylic oligomers; and / or The mass ratio of the organic precursor to the lithium nickel manganese cobalt oxide powder is (0.1-8):100; and / or The mixing process includes at least one of wet stirring, spray drying or dry mixing, and ball milling; wherein the wet stirring uses deionized water or a low-volatility solvent as the dispersion medium.

3. The preparation method according to claim 1, characterized in that, Before step S100, the method further includes: S001. The lithium nickel manganese cobalt oxide powder is dried to make the moisture content of the lithium nickel manganese cobalt oxide powder 0.1-0.5wt%.

4. The preparation method according to claim 1, characterized in that, In step S100, the organic precursor also includes functional additives; The functional additive includes at least one of phosphorus-containing precursors, aluminum-containing precursors, boron-containing precursors, or organometallic complexes, and the amount of the functional additive is 0.01-2.0 wt%.

5. The preparation method according to claim 1, characterized in that, In step S200, the mixture is filled into an inner liner, the inner liner having a filling density of 40-70%, and the inner liner comprising at least one of a metal inner mold, a graphite inner mold, or a can-in-can structure.

6. The preparation method according to claim 1, characterized in that, In step S200, the warm isostatic pressing process is carried out in an inert atmosphere, and the warm isostatic pressing process includes a first stage and a second stage; The pressure in the first stage is 10-50 MPa, the temperature is 300-420℃, and the time is 1-5 min; The second stage has a pressure of 50-200 MPa, a temperature of 350-450℃, and a time of 10-60 min.

7. The preparation method according to claim 1, characterized in that, In step S200, the cooling process and the decompression process are carried out in an inert atmosphere; The cooling process includes cooling to room temperature at a cooling rate of 3-8°C / min; The pressure reduction process includes: performing a first pressure reduction at a rate of 5-20 MPa / min, followed by a second pressure reduction at a rate of 0.5-5 MPa / min, until the pressure drops to atmospheric pressure.

8. The preparation method according to claim 1, characterized in that, Following step S200, the method further includes: S300. The lithium nickel manganese cobalt oxide material is subjected to post-annealing treatment at 200-300°C for 30-180 minutes under an inert atmosphere.

9. A lithium nickel manganese cobalt oxide material with high cycle stability, characterized in that, The lithium nickel manganese cobalt oxide material is prepared by the method of any one of claims 1-8, and the lithium nickel manganese cobalt oxide material includes active particles and a carbon coating layer covering at least a portion of the surface of the active particles; The chemical formula of the lithium nickel manganese cobalt oxide material is LiNi. x Mn y Co z O2, and 0 <x<1、0<y<1、0<z<1,x+y+z=1。 10. The lithium nickel manganese cobalt oxide material according to claim 9, characterized in that, The active particles have a D50 of 5-15 μm, and the carbon coating layer has a thickness of 0.5-50 nm.

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