Preparation method of secondary granulated oxidized-unchanged graphite composite coated negative electrode material

Abstract

The application relates to the technical field of lithium ion battery negative electrode material preparation, and discloses a preparation method of secondary granulation oxidized-unoxidized graphite composite coated negative electrode material, which comprises the following steps: adsorbing trace mild oxidized graphite powder on the surface of unoxidized spherical graphite basic elements to form a solid-phase precursor; constant-temperature treatment in a specific rheological locking temperature interval; using oxygen-containing functional groups on the surface of the oxidized graphite to induce dehydrogenation and polycondensation of pitch at the contact interface to construct a semi-coking pinning shell; high-temperature carbonization and graphitization; and in-situ reduction of the oxidized graphite and retention of a micro interlocking structure; the application solves the rheological mismatch problem in the pitch heat treatment process by using an interface in-situ tackification mechanism, realizes atomic-level close adhesion and structure interlocking of the coating layer and the base material, and improves the structural stability and rate performance of the material in a long cycle process.

Description

Technical Field

[0001] This invention relates to a method for preparing a composite coated anode material of oxidized unoxidized graphite through secondary granulation, belonging to the technical field of lithium-ion battery anode material preparation. Background Technology

[0002] Currently, lithium-ion batteries are widely used in consumer electronics, electric vehicles, and energy storage due to their high energy density and long cycle life. To improve battery energy density, the industry generally uses highly crystalline natural or artificial graphite as the core aggregate, and coal tar pitch as a binder and coating precursor. A secondary granulation process is used to construct spherical particles with higher isotropic properties, improving the material's rate performance and processing performance. However, driven by the dual demands of high energy density and long cycle life, existing secondary granulation processes face severe challenges related to thermal and hygroscopic rheological mismatch. Highly crystalline graphite has extremely low surface energy, exhibiting… Currently, coal tar pitch, as a coating precursor, exhibits high liquefaction. It has a wide low-viscosity liquid phase temperature range between its softening point and the thermal condensation initiation temperature. The dynamic viscosity of the molten pitch is extremely low. Driven by the principle of minimum surface energy in thermodynamics, the low-viscosity liquid phase pitch tends to undergo dewetting and self-aggregation spheroidization on the surface of inert graphite. The pitch film shrinks, fractures, and aggregates into isolated droplets before solidifying into coke. Existing technologies attempt to improve the bonding force by increasing the amount of pitch or introducing an oxidizing atmosphere for pretreatment. The former leads to an excessively large specific surface area and reduced initial efficiency, while the latter destroys the integrity of the graphite lattice and severely impairs conductivity and rate performance.

[0003] To address this interfacial bonding challenge, existing technologies employ strong oxidation pretreatment or complex liquid-phase composite processes. For instance, Chinese invention patent CN106129343B discloses a method for preparing graphene-titanium dioxide microspheres, which enhances the bonding force between the carbon matrix and the active material through strong oxidation treatment with concentrated sulfuric acid and potassium permanganate, followed by spray drying. However, this approach based on strong chemical erosion modification has inherent flaws: the strong oxidation process severely damages the long-range order and integrity of the graphite lattice, leading to a significant decrease in the bulk electronic conductivity of the material; the introduction of surfactants and residual unreduced insulating functional groups forms a high impedance barrier at the interface, causing severe polarization of the material under high-rate charge and discharge. Furthermore, the liquid-phase dispersion and drying preparation process is complex and energy-intensive, making it difficult to balance the intrinsic conductivity advantage of highly crystalline graphite with the interfacial bonding strength.

[0004] Therefore, the technical problem to be solved by this invention is how to avoid rheological mismatch during the asphalt heat treatment process without destroying the intrinsic conductive structure of highly crystalline graphite, and to achieve atomic-level tight bonding and structural interlocking between the coating layer and the substrate. Summary of the Invention

[0005] To address the problems mentioned in the background art, the technical solution of the present invention is as follows: A method for preparing a secondary granulation oxidized unoxidized graphite composite coated anode material, comprising the following steps:

[0006] Step S1: Constructing a heterogeneous solid-phase precursor. Unoxidized spherical graphite particles with a D50 particle size of 8 to 12 micrometers, lightly oxidized graphite micropowder with a D50 particle size of 1 to 3 micrometers and a surface oxygen content of 4.5% to 6.5% by mass, and solid coal tar pitch powder with a softening point of 100 to 110 degrees Celsius are fed into a mechanical fusion device and dry mechanical fusion is performed at a speed of 2500 to 3000 rpm. The lightly oxidized graphite micropowder is dispersed and adsorbed on the surface and gaps of the unoxidized spherical graphite particles by means of van der Waals forces to form a precursor mixture.

[0007] Step S2: Perform interface rheological locking and in-situ thickening. Place the precursor mixture in a protective atmosphere and heat it to the rheological locking temperature range of 280°C to 320°C at a heating rate of 2°C / min to 5°C / min. Maintain the temperature within this range for 3 to 5 hours. Utilize the oxygen-containing functional groups on the surface of the lightly oxidized graphite micropowder as solid-phase Lewis acid sites to induce preferential dehydrogenation polycondensation reaction in the melt of the solid coal tar powder at the contact interface. Before the macroscopic thermal polycondensation of the solid coal tar powder bulk occurs, a high-viscosity semi-coking pinned shell layer is constructed in-situ on the surface of the unoxidized spherical graphite particles.

[0008] Step S3 completes the structural densification and in-situ reduction and repair. The material treated in step S2 is heated to 1000 to 1100 degrees Celsius for carbonization treatment, so that the remaining asphalt components are transformed into an amorphous carbon coating layer. Graphitization treatment is carried out at 2800 to 3000 degrees Celsius to reduce the slightly oxidized graphite powder in situ to a highly crystalline graphite phase and retain the microscopic interlocking topology established by the semi-coking pinned shell layer formed in step S2.

[0009] Preferably, in step S1, the specific mass ratio of unoxidized spherical graphite particles, lightly oxidized graphite micropowder, and solid coal tar powder is: 92 to 94 parts by weight of unoxidized spherical graphite particles, 3 to 5 parts by weight of lightly oxidized graphite micropowder, and 3 to 6 parts by weight of solid coal tar powder; the surface oxygen content of the lightly oxidized graphite micropowder is prepared by the Hummers method and controlled to a range of 4.5% to 6.5% by a washing process, which is sufficient to provide the active site density required for interfacial crosslinking and does not produce structural defects that damage conductivity after graphitization treatment in step S3.

[0010] Preferably, the rheological locking temperature range in step S2 is limited to a range higher than the softening point of the solid coal tar powder and lower than the thermal weight loss initiation temperature of the solid coal tar powder; the dehydrogenation polycondensation reaction establishes a viscosity gradient decreasing from the contact interface to the solid coal tar powder bulk during the isothermal holding period, and the interfacial tension resistance generated by this viscosity gradient is greater than the dewetting retraction force of the molten pitch on the surface of the unoxidized spherical graphite particles.

[0011] Preferably, during the graphitization process in step S3, the lightly oxidized graphite micropowder undergoes lattice rearrangement and defect repair, and its interlayer spacing d002 is reduced from more than 0.340 nanometers in the oxidized state to less than 0.336 nanometers; the graphite phase after in-situ reduction is embedded as a highly conductive node between the amorphous carbon coating layer and the unoxidized spherical graphite particles to form an electron transport channel.

[0012] Preferably, the addition amount M of lightly oxidized graphite powder LOG The amount M added with solid coal tar powder Pitch The relationships between them satisfy a correlation based on interface catalytic efficiency matching, which is defined by the following formula: , of which O content K represents the surface oxygen content (by mass percentage) of lightly oxidized graphite micropowder. c The reactivity constant of the aromatic hydrocarbon component in solid coal tar pitch powder is a constant that characterizes the tendency of pitch to undergo polycondensation under Lewis acid catalysis. The value ranges from 0.05 to 0.08. This correlation is used to ensure that the number of acidic sites at the interface and the amount of contact between pitch molecules reach stoichiometric equilibrium.

[0013] Preferably, the mechanical fusion in step S1 is carried out in a high-speed mixing device with a circulating cooling jacket, and the material temperature during the process is controlled to be below 60 degrees Celsius to prevent the solid coal tar pitch powder from softening or agglomerating prematurely during the physical adsorption stage; the shear force applied by mechanical fusion is sufficient to break the soft agglomerates of the lightly oxidized graphite micropowder so that it is anchored in a monodisperse state at the micropores or steps on the surface of the unoxidized spherical graphite particles.

[0014] Preferably, in step S2, before heating to the rheological lock-in temperature range, a liquid phase wetting stage is also included: heating to 150 degrees Celsius at a rate of 2 degrees Celsius / minute to 3 degrees Celsius / minute and holding at a constant temperature for 30 minutes to 60 minutes. This stage is used to completely melt the solid coal tar pitch powder and fill the microscopic gaps between the lightly oxidized graphite micropowder and the unoxidized spherical graphite particles under the action of capillary force to establish the physical contact basis of the contact interface.

[0015] Preferably, the coking value of the solid coal tar pitch powder is greater than or equal to 55%, and the content of quinoline insoluble matter present as an impurity in the solid coal tar pitch powder is less than or equal to 1.0%; the tap density of the unoxidized spherical graphite particles is greater than or equal to 0.95 g / cm³; the preparation method is a completely dry solid-phase treatment process that does not involve any steps of introducing or removing liquid solvents, dispersants or liquid phase binders.

[0016] Preferably, step S3 graphitization is performed using an Atchison graphitization furnace or an internal series graphitization furnace. The in-situ reduction and graphitization process eliminates the interfacial resistance caused by the introduction of slightly oxidized graphite powder in the precursor mixture, so that the conductivity of the obtained negative electrode material powder is greater than or equal to the conductivity of the control sample without the addition of slightly oxidized graphite powder.

[0017] Preferably, the semi-coking studded shell layer in step S2 is transformed into an inlay structure after the high-temperature treatment in step S3. The inlay structure is characterized by in-situ reduced graphite microcrystals acting as rivet nodes physically interspersed between the base surface of the unoxidized spherical graphite particles and the outer amorphous carbon layer. This inlay structure can suppress the peeling of the coating layer caused by volume expansion during the lithium ion insertion and extraction process of the negative electrode material.

[0018] Compared with the prior art, the beneficial effects of the present invention are:

[0019] 1. In the secondary granulation oxidation process, an in-situ interfacial thickening mechanism is introduced through carbon source heat treatment to solve the problem of microscopic peeling and discontinuity of the asphalt coating layer caused by the low surface energy of the highly crystalline graphite matrix. The oxygen-containing functional groups on the surface of slightly oxidized graphite are used as solid-phase catalytic sites. When the asphalt body is in the low viscosity liquid phase temperature range, the asphalt molecules at the contact interface are induced to preferentially undergo dehydrogenation and polycondensation reactions, and a high viscosity anti-flow semi-coking pinning shell layer is rapidly constructed on the surface of the graphite matrix. The micromorphology of the coating layer is locked before the asphalt undergoes macroscopic thermodynamic shrinkage or self-aggregation and spheroidization. The process path of shaping before carbonization ensures that the amorphous carbon coating layer and the graphite substrate form an atomic-level tight bond and stress interlock, which improves the structural integrity of the negative electrode material during the long cycle charge and discharge volume expansion process and inhibits particle pulverization and active material shedding.

[0020] 2. To achieve enhanced synergy and decoupling of conductive network construction and interface bonding, unlike traditional technologies that introduce oxide functional groups that destroy conductivity, this method utilizes the chemical activity of lightly oxidized graphite during the low-temperature granulation stage to construct a supporting framework. The thermal reduction characteristics of the subsequent high-temperature graphitization process are then used to transform the oxidized components into a highly crystalline graphite phase. Ultimately, the original oxidation-induced components in the negative electrode material are transformed in situ into a graphite structure with high electronic conductivity, forming a continuous electron transport channel with the outer amorphous carbon and the core graphite units. This eliminates the interfacial impedance caused by the introduction of insulating modifiers, enhances the mechanical strength of the particles, and retains the intrinsic high-rate kinetic performance and lithium-ion transport efficiency of graphite materials.

[0021] 3. It has excellent process adaptability and engineering implementation value. Unlike traditional modification methods that rely on complex liquid phase coating or expensive organic crosslinking agents, it is based on the chemical properties of conventional carbonaceous precursors. It establishes rheological locking steps through the time sequence reconstruction of heat treatment process, and realizes the directional control of microstructure in existing industrial-grade rotary kilns or graphitization equipment. It reduces the sensitivity of the coating process to the surface state of graphite raw materials and the batch stability of asphalt, avoids batch-to-batch quality fluctuations caused by differences in raw material wettability, improves the yield and product consistency of high-performance composite anode material preparation process, and meets the actual needs of large-scale industrial production. Attached Figure Description

[0022] Figure 1 This is a flow chart of the secondary granulation composite coating process based on the interface rheological locking mechanism of the present invention.

[0023] Figure 2 This is a graph showing the effect of oxygen content on the surface of lightly oxidized graphite on key performance indicators of the material.

[0024] Figure 3 This is a schematic diagram of the material flow and operation sequence logic of each stage of the preparation process of the present invention. Detailed Implementation

[0025] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0026] This invention provides a method for preparing a composite coated anode material using secondary granulation of oxidized and unoxidized graphite, comprising three core stages: constructing a heterogeneous solid-phase precursor, performing interfacial rheological locking and in-situ thickening, and completing structural densification and in-situ reduction and repair. Unoxidized spherical graphite particles are used as the core aggregate, lightly oxidized graphite micropowder is used as an interfacial rheological inducer, and solid coal tar pitch powder is used as the carbon source precursor. By utilizing the oxygen-containing functional groups on the surface of lightly oxidized graphite to induce preferential dehydrogenation and polycondensation of the interfacial pitch within a specific temperature range, a semi-coking pinned shell layer is constructed. During high-temperature treatment, the inducer is in-situ reduced to a highly conductive graphite phase, achieving atomic-level interlocking between the coating layer and the substrate.

[0027] To address the issue that highly crystalline graphite surfaces exhibit significant hydrophores, leading to the tendency of molten bitumen to undergo self-agglomeration and interfacial slippage before carbonization, this method employs a step of constructing a heterogeneous solid-phase precursor, selecting a material with a tapped density greater than or equal to 0.95 g / cm³. 3 And D 50Unoxidized spherical graphite particles with a particle size of 8μm to 12μm are used as the main substrate to ensure the high compaction density and high capacity characteristics of the anode material. D... 50 Lightly oxidized graphite powder with a particle size of 1 μm to 3 μm was used as a rheology inducer. This powder was prepared using the Hummers method and controlled through a washing process to strictly limit the surface oxygen content (mass fraction) to the range of 4.5% to 6.5%. This oxygen content range was set because when the oxygen content is below 4.5%, the density of Lewis acid active sites on the surface is insufficient to initiate effective interfacial catalytic crosslinking; when the oxygen content is above 6.5%, excessive oxygen-containing functional groups will cause structural breakage and damage to the conductive network during subsequent high-temperature treatment. Solid coal tar powder with a softening point of 100℃ to 110℃, a coking value greater than or equal to 55%, and a quinoline insoluble content less than or equal to 1.0% was also selected as a rheology inducer. The binder and coating source are added to a high-speed mixing device with a circulating cooling jacket according to the above three components in the mass ratio. The unoxidized spherical graphite particles are 92 to 94 parts by weight, the lightly oxidized graphite powder is 3 to 5 parts by weight, and the solid coal tar pitch powder is 3 to 6 parts by weight. The mechanical fusion speed is set to 2500 to 3000 rpm, the processing time is 15 to 20 minutes, and the material temperature is controlled below 60°C to prevent the pitch from softening and agglomerating prematurely. This mechanical fusion process uses strong shear force to break the soft agglomerates of the lightly oxidized graphite powder, so that it is monodisperse and adsorbed by van der Waals forces and anchored at the micropores or steps on the surface of the unoxidized spherical graphite particles to form a precursor mixture.

[0028] Based on the fact that molten asphalt is prone to interfacial dewetting and shrinkage in the low-viscosity liquid phase temperature range of ℃ to 350℃, this method then performs interfacial rheological locking and in-situ thickening steps. The precursor mixture is placed in a nitrogen protective atmosphere and heated to 150℃ at a heating rate of 2℃ / min to 3℃ / min, and held at this temperature for 30 to 60 minutes. During this liquid phase wetting stage, the capillary force after the asphalt is completely melted is used to fill the microscopic gaps between the lightly oxidized graphite powder and the unoxidized spherical graphite particles, establishing the physical connection basis of the contact interface. The temperature is then increased to the rheological locking temperature range of 280℃ to 320℃ at a rate of 2℃ / min to 5℃ / min, and held at this temperature for 3 to 5 hours. The selection of this temperature range is based on the rheological properties of asphalt. Its temperature is higher than the softening point of asphalt but lower than the starting temperature of macroscopic thermal condensation of the asphalt bulk. During this isothermal period, the carboxyl and hydroxyl groups adsorbed on the surface of the lightly oxidized graphite powder at the interface act as solid-phase Lewis acid sites, reducing the activation energy of the dehydrogenation condensation reaction of asphalt molecules at the contact interface. This induces the interfacial asphalt to undergo cross-linking reaction preferentially over the bulk asphalt. This reaction establishes a viscosity gradient decreasing from the contact interface to the asphalt bulk at the microscopic level, causing the asphalt layer adjacent to the graphite surface to rapidly transform into a high-viscosity semi-coke state, forming a pinned shell layer. The interfacial tension resistance generated by this semi-coke pinned shell layer is greater than the dewetting shrinkage force of molten asphalt on the surface of unoxidized spherical graphite particles, thereby locking the microstructure of the coating layer and preventing asphalt film rupture and spheroidization. The amount of lightly oxidized graphite powder added, M... LOG The amount M added with solid coal tar powder Pitch Satisfying the correlation based on interface catalytic efficiency matching: O content K represents the surface oxygen content (by mass percentage) of lightly oxidized graphite micropowder. c The reactivity constant of the aromatic hydrocarbon component in solid coal tar pitch powder is between 0.05 and 0.08. This formula ensures that the number of acidic sites at the interface and the amount of contact between pitch molecules reach stoichiometric equilibrium.

[0029] To address the potential decrease in conductivity and increase in interfacial impedance caused by the introduction of oxides, and considering the final structural strength of the material, this method concludes with a densification and in-situ reduction repair step. The rheology-locked material is heated to 1000℃-1100℃ under a protective atmosphere for carbonization, transforming the remaining asphalt components into an amorphous carbon coating layer. The material is then fed into an Atchison graphitization furnace or an internal series graphitization furnace for graphitization at ultra-high temperatures of 2800℃-3000℃. During this process, the slightly oxidized graphite micropowder undergoes lattice rearrangement and defect repair, reducing the interlayer spacing d. 002The graphite particles are reduced from above 0.340 nm in the oxidized state to below 0.336 nm, and then in situ reduced to a highly crystalline graphite phase. This process eliminates the electron transport barrier caused by the introduction of oxygen-containing functional groups in the precursor, resulting in a negative electrode material powder with an electrical conductivity greater than or equal to that of the control sample without the addition of slightly oxidized graphite micropowder. The semi-coking pinned shell layer formed in the early stage is transformed into an embedded structure after high-temperature treatment. In this structure, the in-situ reduced graphite microcrystals act as highly conductive rivet nodes, physically interpenetrating and embedding between the basal surface of the unoxidized spherical graphite particles and the outer amorphous carbon layer, forming an electron transport channel. This microscopic interlocking topology disperses the anisotropic stress caused by lithium ion insertion and extraction during charging and discharging, and suppresses the peeling of the coating layer caused by the volume expansion of the negative electrode material.

[0030] Reactivity constant K c Based on the torque rheological testing procedure, the batch of solid coal tar pitch powder to be tested was premixed with standard lightly oxidized graphite powder at a mass ratio of 10:1 and placed in a mixing chamber. The torque versus time curve was recorded under shear conditions of 300 degrees Celsius and 60 rpm. The slope S was calculated from the linear growth segment of the curve. sample According to formula K c equals S sample Divide by S ref Calculated by multiplying by 0.065, where S ref To obtain the torque growth slope using standard reference asphalt under identical conditions, eliminate interference from equipment differences and environmental fluctuations in stoichiometric ratio calculations, and ensure that the reaction kinetic matching degree at the interface of different batches of raw materials is within the range defined by the correlation formula, the rheological locking temperature range is dynamically adjusted based on the thermal analysis characteristic data of the precursor mixture. Precursor mixture samples are extracted and subjected to differential scanning calorimetry (DSC) analysis at a rate of 10°C / min under a nitrogen atmosphere to identify the exothermic peak initiation temperature T in the range of 280°C to 350°C. onset The temperature of the subsequent isothermal treatment process is set to T. onset Subtracting 5 to 10 degrees Celsius, by anchoring the process temperature to the actual reaction initiation point of the material, ensures that oxygen-containing functional groups induce preferential cross-linking at the interface before macroscopic bulk thermal condensation of the asphalt melt, forming a stable semi-coke pinned shell layer; the oxygen content on the surface of the lightly oxidized graphite micropowder is O content Calibration refers to the mass fraction of chemically bound oxygen after removing physically adsorbed water. Before testing, the sample is dried to constant weight in an environment with a vacuum degree of less than 100 Pa and a temperature of 80 degrees Celsius. The sample is then measured using an infrared carbon-sulfur analyzer or X-ray photoelectron spectroscopy to eliminate the nonlinear interference of adsorbed water on the calculation of Lewis acid site density caused by environmental humidity fluctuations.

[0031] Example 1: In the industrial preparation of high-performance power battery anode materials, this example addresses the technical challenges of high surface inertness of highly crystalline graphite substrates and the tendency of conventional asphalt coating processes to cause dewetting spheroidization and structural pulverization. It provides a preparation example based on an interfacial rheological locking mechanism. By strictly controlling the specifications of each component and process parameters, a composite anode material with an interfacial interlocking structure is stably prepared on an industrial-grade production line, with a tap density of 1.05 g / cm³. 3 And D 50 Unoxidized natural graphite spherical particles with a particle size of 10.5 μm were used as the main aggregate to ensure a high reversible capacity. D was selected. 50 Lightly oxidized graphite powder with a particle size of 2.2 μm was used as a rheology inducer. This powder was prepared by the Hummers method and subsequently washed and purified. The surface oxygen content mass fraction was determined to be 5.8% by elemental analysis. Medium-temperature coal tar pitch powder with a softening point of 108℃, a coking value of 58%, and a quinoline insoluble content of 0.4% was selected as the coating precursor. 93 kg of unoxidized natural graphite spherical particles, 4 kg of lightly oxidized graphite powder, and 4 kg of medium-temperature coal tar pitch powder were put into a high-speed mechanical fusion machine. The rotation speed was set to 2800 rpm, the processing time was 18 minutes, and the cooling water temperature was controlled below 25℃. This allowed the lightly oxidized graphite powder and coal tar pitch powder to be monodispersed and anchored on the surface of the graphite aggregate by mechanical shear force, forming a uniform precursor mixture.

[0032] The precursor mixture was placed in a nitrogen-protected rotary kiln to perform interfacial rheological locking and in-situ thickening processes. The heating program was set as follows: first, the temperature was increased to 150°C at a rate of 2.5°C / min and held for 45 minutes to allow the asphalt to completely melt and wet the interparticle gaps; then, the temperature was increased to 300°C at a rate of 3°C / min and held at this rheological locking temperature for 4 hours. During this isothermal stage, the oxygen-containing functional groups on the surface of the lightly oxidized graphite powder catalyzed the preferential dehydrogenation and polycondensation of asphalt molecules at the contact interface. While the asphalt matrix remains fluid, a high-viscosity, semi-coke pinned shell layer is constructed in situ on the surface of the graphite substrate. This shell layer effectively resists the surface tension shrinkage of the molten asphalt, locking the coating morphology. Finally, the rheology-locked material is carbonized by heating to 1050℃ at 5℃ / min and holding for 2 hours in a nitrogen atmosphere, and then sent to a graphitization furnace for high-temperature treatment at 2900℃. During this process, oxygen atoms in the lightly oxidized graphite micropowder are completely removed and transformed in situ into interlayer spacing d. 002The high-crystallinity graphite phase of 0.3356 nm eliminates the interfacial electron transport barrier, resulting in a composite anode material exhibiting a unique micro-interlocking topology. The in-situ reduced graphite microcrystals act as conductive rivets embedded between the amorphous carbon layer and the graphite substrate, enhancing interfacial bonding and electronic conductivity. The material achieves an initial charge-discharge efficiency of 94.5% at 1C rate, and its capacity retention rate remains above 92% after 2000 full charge-discharge cycles.

[0033] Example 2: This example constructs a comprehensive verification platform covering the characterization of the physicochemical properties of materials and the testing of the electrochemical performance of the full battery, simulating the real stress environment of electric vehicle power batteries during long-cycle and high-rate charge-discharge processes. The composite anode material prepared in Example 1 was selected as the sample group of this invention. To construct a convincing multi-dimensional control system, three control groups were set up: Control group 1 used the same unoxidized natural graphite spherical particles and solid coal tar powder, but without the addition of lightly oxidized graphite micropowder. It was simply mechanically mixed and then subjected to the same carbonization and graphitization treatment, aiming to verify the role of rheology inducers in interfacial bonding. The key role of the process; Control group 2 used the same raw material ratio, but omitted the isothermal rheological locking step from 280℃ to 320℃ and directly carried out heating carbonization and graphitization, aiming to verify the decisive influence of the isothermal rheological mutation process on the integrity of the coating structure; Control group 3 used the same process flow, but replaced the slightly oxidized graphite powder with an equal amount of ordinary graphite powder that had not been oxidized, aiming to verify the catalytic necessity of surface oxygen-containing functional groups as solid-phase Lewis acid sites. The graphitization treatment conditions of all sample groups were strictly kept consistent, that is, treated at 2900℃, to eliminate the influence of temperature difference on the degree of graphitization.

[0034] The microstructure and interfacial bonding were characterized using scanning electron microscopy (SEM) to observe the surface morphology and cross-sectional structure of each sample group. The sample group of this invention showed a continuous, dense, and uniformly thick carbon coating layer. The cross-sectional images clearly revealed that the in-situ reduced graphite microcrystals were deeply embedded between the substrate and the amorphous carbon layer, forming a tight mechanical interlocking structure. In contrast, the particle surfaces of control group 1 and control group 3 showed obvious asphalt dewetting phenomenon, the coating layer was distributed in an island-like manner, and microcracks and peeling gaps between the coating layer and the substrate were observed at the cross-section. Although the coating coverage of control group 2 was slightly better than that of control group 1, the coating layer thickness was extremely uneven and lacked deep pinning nodes. Furthermore, the powder conductivity was measured by a powder resistivity tester under a pressure of 12 MPa. The results showed that the powder conductivity of the sample group of this invention was 18.5 S / cm, which was higher than that of control group 1 (14.2 S / cm) and control group 2 (15.6 S / cm), proving the effectiveness of the efficient electron transport channel constructed by the in-situ reduced graphite phase, and that the conductivity was not impaired by the introduction of the oxide precursor.

[0035] The core electrochemical performance verification was conducted using CR2032 coin cell half-cells and pouch cells. In the coin cell test, lithium metal sheets were used as the counter electrode, and charge-discharge tests were performed at a rate of 0.1C. Referring to Table 1, the sample group of this invention exhibited the best initial coulombic efficiency and reversible specific capacity, indicating that the dense coating layer effectively suppressed the side reactions of the electrolyte on the graphite surface. In the long-cycle stability test of the pouch cell, the negative electrode material of each sample group was matched with the same lithium cobalt oxide positive electrode, and cycle life tests were performed at a 1C charge-discharge rate and a constant temperature environment of 25℃. The data in Table 1 clearly show that this invention… After 2000 cycles, the capacity retention rate of the invention sample was still as high as 92.4%, and no obvious pulverization or peeling was found after the electrode was disassembled. In contrast, the capacity retention rates of control groups 1, 2 and 3 were only 81.5%, 85.3% and 83.1%, respectively, and all showed varying degrees of active material shedding. This performance difference directly proves that the semi-coking pinned shell layer constructed by the interface rheology locking process and its transformed micro-interlocking structure can effectively resist the volume expansion stress caused by repeated lithium ion insertion and extraction, thereby significantly improving the structural stability and cycle life of the material.

[0036] Table 1: Comparison of Electrochemical Performance Test Results for Each Sample Group

[0037]

[0038] This embodiment utilizes lightly oxidized graphite micropowder as a rheology inducer, combined with a constant-temperature rheology locking process, to solve the problem of coating highly crystalline graphite pitch, achieving atomic-level tight adhesion between the coating layer and the substrate, and improving the cycle stability and rate performance of the anode material without sacrificing conductivity.

[0039] Example 3: This example combines Figures 1 to 3 The preparation method of secondary granulation and oxidation of unoxidized graphite composite coated anode material is described, such as... Figure 1As shown, the process begins with the preparation of raw material components. 92 to 94 parts of unoxidized spherical graphite, 3 to 6 parts of solid coal tar pitch, and 3 to 5 parts of lightly oxidized graphite micropowder with an oxygen content of 4.5% to 6.5% are mixed and fed into step S1 to construct a heterogeneous solid-phase precursor. Monodisperse adsorption and van der Waals anchoring are achieved through high-speed mechanical fusion at a rotation speed of 2500 to 3000 rpm and a temperature below 60°C. This is followed by step S2, a pre-liquid phase wetting stage, where physical contact is established by capillary filling with molten pitch at a constant temperature of 150°C for 30 to 60 minutes. Then, step S2, the core stage of interfacial rheological locking and in-situ thickening, commences. In the first stage, the asphalt is kept at a constant temperature of 280℃ to 320℃ for 3 to 5 hours. The Lewis acid sites are used to catalyze preferential dehydrogenation and polycondensation to construct a semi-coking pinned shell layer. Then, the structure is densified by carbonization in step S3. The asphalt is converted into an amorphous carbon coating layer at 1000℃ to 1100℃. Then, the graphitization in step S3 is carried out in-situ reduction and repair. At 2800℃ to 3000℃, the lattice rearrangement makes d002 < 0.336nm, eliminating interfacial impedance and forming a micro-interlocked topology. Finally, a secondary granulation composite coated anode material with atomic-level tight bonding, inhibiting coating peeling, high electronic conductivity and excellent cycle and rate performance is obtained.

[0040] like Figure 2 As shown, the horizontal axis represents the surface oxygen content, ranging from 3% to 7%; the left vertical axis represents the efficiency or retention rate, ranging from 75% to 95%; and the right vertical axis represents the conductivity, ranging from 10 to 20 S / cm. The graph contains three curves: the solid line represents the initial coulombic efficiency, the dashed line represents the capacity retention rate after 2000 cycles, and the dotted line represents the powder conductivity. All three indicators show a trend of first increasing and then decreasing with changes in surface oxygen content, and all reach their peak values ​​at approximately 5% surface oxygen content. The peak value of the initial coulombic efficiency is close to 95%, the peak value of the capacity retention rate exceeds 92%, and the peak value of the powder conductivity is 18.5 S / cm. Figure 3 As shown, the time sequence logic of this preparation process spans five stages: raw material preparation, precursor construction, rheological locking, carbonization and graphitization, and finished product testing. In the raw material preparation stage, unoxidized spherical graphite particles, lightly oxidized graphite micro powder, and solid coal tar powder are added sequentially. In the precursor construction stage, dry mechanical fusion is performed and the precursor mixture is transported. Then, in the rheological locking stage, liquid phase wetting treatment, rheological locking temperature isothermal treatment, and semi-coking pinned shell layer are carried out sequentially. After that, the locked material is transported to the carbonization and graphitization stage, where it undergoes carbonization treatment to form an amorphous carbon layer and graphitization treatment for in-situ reduction, finally forming a micro-interlocked structure and outputting a composite negative electrode material. Finally, it enters the finished product testing stage to complete the electrochemical performance test.

[0041] Example 4: In industrial continuous production processes, solid coal tar pitch powder, as a bulk chemical raw material, exhibits batch-to-batch fluctuations in the distribution and reactivity of aromatic hydrocarbon components, which in turn prevents the fixed mass ratio from being consistently maintained. To address the engineering challenge within this optimal reaction kinetic window, this embodiment constructs a set of procedures for calibrating the reactivity constant and dynamically refining the formulation based on torque rheology. This procedure is configured to be executed before each batch of solid coal tar pitch powder is added to the main mixing process. During the calibration stage, 50g of the solid coal tar pitch powder sample from the batch to be tested is premixed with 5g of lightly oxidized graphite micropowder (with a known surface oxygen content of 5.5%) used as a standard reference. The mixture is then placed in the mixing chamber of a Haake torque rheometer with precise temperature control. The mixing chamber temperature is set to 300℃ and the rotor speed to 60rpm. The rheological curve of the mixture's torque over time is recorded in real time. During the isothermal shearing process, as the interfacial dehydrogenation and polycondensation reaction proceeds, the system viscosity gradually increases, resulting in a continuous increase in output torque. This procedure defines the slope of the linear growth segment of the rheological curve as the reaction rate characterization value, and uses the formula... Calculate the reactivity constant K of this batch of asphalt. c S sample S is the measured slope of the torque growth of the sample under test. ref K represents the torque growth slope of the reference asphalt sample. ref The preset activity constant of the reference asphalt is set to 0.065.

[0042] Obtain a definite K c After the numerical values ​​are calculated, the system establishes the association relationships defined in the claims. The precise mass M of lightly oxidized graphite powder required to match 100 parts by weight of solid coal tar pitch powder in the current production batch is calculated in reverse. LOG (The target value is set at the stoichiometric equilibrium point of 1.0). When the K value of a certain batch of asphalt is measured... c When K is 0.075 (high activity), the calculated amount of lightly oxidized graphite powder added should be reduced accordingly to avoid increased brittleness caused by excessive local cross-linking; if K c If the value is 0.055, the amount added needs to be increased to ensure sufficient pinning point density. Through this closed-loop control based on real-time rheological data detection-calculation-correction, it is ensured that no matter how the anisotropy of the raw materials fluctuates, the acidic catalytic sites at the interface and the asphalt active components are always in a thermodynamically optimal matching state when each batch of composite precursor enters the rheological locking temperature range.

[0043] Example 5: To address the issue that ambient humidity affects the adsorbed water content of oxygen-containing functional groups on the surface of lightly oxidized graphite micropowder in different climate zones or seasonal production cycles, leading to unexpected fluctuations in the catalytic activity of Lewis acid sites, this example constructs a pre-processing procedure for microwave-assisted vacuum drying and surface state normalization as a standardized pretreatment unit for the main production process.

[0044] In the normalization process, the lightly oxidized graphite powder to be used is placed in a microwave vacuum drying reactor with a stirring function. The system is evacuated to below 100 Pa, and pulsed microwave radiation with a frequency of 2450 MHz and a power density of 0.5 W / g is applied while the stirring paddle continuously tumbles at a speed of 30 rpm. The microwave energy is preferentially absorbed by water molecules between graphite layers and on the surface, achieving rapid and non-contact deep dehydration. By monitoring the pressure recovery rate and exhaust gas humidity in the reactor in real time, the dehydration endpoint is determined when the monitored pressure recovery rate is below 5 Pa / min and the exhaust gas dew point temperature is below -40℃. While maintaining the vacuum, dry nitrogen is introduced into the reactor until atmospheric pressure is reached, and the treated powder is directly transported to the subsequent mechanical fusion equipment under nitrogen protection. This effectively eliminates the interference of environmental humidity fluctuations on catalyst activity and ensures the consistency of the starting conditions for the interfacial rheological locking reaction. Batch products produced under different environmental humidity conditions can stably obtain the expected micro-interlocked structure and electrochemical performance.

[0045] Example 6: To address the issue of inconsistent interfacial reaction levels caused by fluctuations in the rheological properties of raw material asphalt batches and non-uniformity of the thermal field distribution in the production line during actual production, this example constructs a standardized procedure for calibrating the interfacial reaction kinetic window and adaptively correcting process parameters. This procedure is executed before each batch of precursor mixture is formally introduced into the rheological locking process, aiming to eliminate the engineering black box introduced by differences in raw material properties and equipment state drift, and ensure the robustness of the interfacial pinning effect. This procedure defines a micro-reactivity calibration process based on offline thermogravimetric-differential scanning calorimetry (TG-DSC). For each new batch of solid coal tar pitch powder and lightly oxidized graphite powder mixture, the temperature is increased to 600℃ at a rate of 10℃ / min under a nitrogen atmosphere. The system automatically analyzes the exothermic peak in the DSC curve located in the range of 280℃ to 350℃ and extracts the onset temperature T of the exothermic peak. onset Peak temperature T peak and the enthalpy of heat release per unit mass ΔH, the procedure is set as follows: if the measured T onset If the deviation from the baseline value (290℃) exceeds ±5℃ or the deviation of ΔH from the baseline value (120J / g) exceeds ±10%, the interfacial reactivity of the batch of raw materials is determined to have drifted.

[0046] Based on the above calibration results, the procedure implements adaptive correction logic for process parameters: if T onsetIf the temperature is below the lower limit of the baseline, it indicates that the reactivity is too high and there is a risk of premature local coking. In this case, the isothermal temperature setpoint of the rheology lockout stage should be lowered by 5°C to 10°C, and the isothermal time should be extended by 30 minutes accordingly to ensure the reaction depth; if T onset If the temperature is higher than the upper limit of the benchmark, it indicates insufficient reactivity. In this case, the constant temperature should be increased by 5°C to 10°C, and the constant temperature time should be shortened by 15 minutes to prevent excessive asphalt loss. If ΔH is lower than the lower limit of the benchmark, it indicates insufficient interfacial crosslinking density. The procedure requires that 0.5% to 1.0% by mass of lightly oxidized graphite powder be added in the precursor batching stage to compensate for the lack of active sites.

[0047] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention.

[0048] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a secondary granulation oxidized unoxidized graphite composite coated anode material, characterized in that, Includes the following steps: Step S1: Constructing a heterogeneous solid-phase precursor. Unoxidized spherical graphite particles with a D50 particle size of 8 to 12 micrometers, lightly oxidized graphite micropowder with a D50 particle size of 1 to 3 micrometers and a surface oxygen content of 4.5% to 6.5% by mass, and solid coal tar pitch powder with a softening point of 100 to 110 degrees Celsius are fed into a mechanical fusion device and dry mechanical fusion is performed at a speed of 2500 to 3000 rpm. The lightly oxidized graphite micropowder is dispersed and adsorbed on the surface and gaps of the unoxidized spherical graphite particles by means of van der Waals forces to form a precursor mixture. Step S2: Perform interface rheological locking and in-situ thickening. Place the precursor mixture in a protective atmosphere and heat it to the rheological locking temperature range of 280°C to 320°C at a heating rate of 2°C / min to 5°C / min. Maintain the temperature within this range for 3 to 5 hours. Utilize the oxygen-containing functional groups on the surface of the lightly oxidized graphite micropowder as solid-phase Lewis acid sites to induce preferential dehydrogenation polycondensation reaction in the melt of the solid coal tar powder at the contact interface. Before the macroscopic thermal polycondensation of the solid coal tar powder bulk occurs, a high-viscosity semi-coking pinned shell layer is constructed in-situ on the surface of the unoxidized spherical graphite particles. Step S3 completes the structural densification and in-situ reduction and repair. The material treated in step S2 is heated to 1000 to 1100 degrees Celsius for carbonization treatment, so that the remaining asphalt components are transformed into an amorphous carbon coating layer. Graphitization treatment is carried out at 2800 to 3000 degrees Celsius to reduce the slightly oxidized graphite powder in situ to a highly crystalline graphite phase and retain the microscopic interlocking topology established by the semi-coking pinned shell layer formed in step S2.

2. The method for preparing a secondary granulation oxidized unoxidized graphite composite coated anode material according to claim 1, characterized in that, In step S1, the specific mass ratio of unoxidized spherical graphite particles, lightly oxidized graphite micro powder, and solid coal tar powder is: 92 to 94 parts by weight of unoxidized spherical graphite particles, 3 to 5 parts by weight of lightly oxidized graphite micro powder, and 3 to 6 parts by weight of solid coal tar powder; the surface oxygen content of the lightly oxidized graphite micro powder is prepared by the Hummers method and controlled to the range of 4.5% to 6.5% by a washing process.

3. The method for preparing a secondary granulation oxidized unoxidized graphite composite coated anode material according to claim 1, characterized in that, The rheological locking temperature range in step S2 is limited to a range above the softening point of the solid coal tar powder and below the thermogravimetric initiation temperature of the solid coal tar powder; the dehydrogenation polycondensation reaction establishes a viscosity gradient decreasing from the contact interface to the solid coal tar powder bulk during the isothermal holding period, and the interfacial tension resistance generated by this viscosity gradient is greater than the dewetting retraction force of the molten pitch on the surface of the unoxidized spherical graphite particles.

4. The method for preparing a secondary granulation oxidized unoxidized graphite composite coated anode material according to claim 1, characterized in that, During the graphitization process in step S3, the lightly oxidized graphite micropowder undergoes lattice rearrangement and defect repair, and its interlayer spacing d002 decreases from more than 0.340 nanometers in the oxidized state to less than 0.336 nanometers. The graphite phase after in-situ reduction serves as a highly conductive node embedded between the amorphous carbon coating layer and the unoxidized spherical graphite particles to form an electron transport channel.

5. The method for preparing a secondary granulation oxidized unoxidized graphite composite coated anode material according to claim 1, characterized in that, The amount of lightly oxidized graphite powder added (M) LOG The amount M added with solid coal tar powder Pitch The relationships between them satisfy a correlation based on interface catalytic efficiency matching, which is defined by the following formula: , of which O content K represents the surface oxygen content (by mass percentage) of lightly oxidized graphite micropowder. c The reactivity constant of the aromatic hydrocarbon component in solid coal tar pitch powder is a constant that characterizes the tendency of pitch to undergo polycondensation under Lewis acid catalysis. The value ranges from 0.05 to 0.

08. This correlation is used to ensure that the number of acidic sites at the interface and the amount of contact between pitch molecules reach stoichiometric equilibrium.

6. The method for preparing a secondary granulation oxidized unoxidized graphite composite coated anode material according to claim 1, characterized in that, In step S1, mechanical fusion is carried out in a high-speed mixing device with a circulating cooling jacket, and the material temperature is controlled to be below 60 degrees Celsius during the process. The shear force applied by mechanical fusion is sufficient to break the soft agglomerates of lightly oxidized graphite powder so that it is anchored in a monodisperse state at the micropores or steps on the surface of unoxidized spherical graphite particles.

7. The method for preparing a secondary granulation oxidized unoxidized graphite composite coated anode material according to claim 1, characterized in that, In step S2, before heating to the rheological lock-in temperature range, a liquid phase wetting stage is also included: heating to 150 degrees Celsius at a rate of 2 to 3 degrees Celsius per minute and holding at that temperature for 30 to 60 minutes. This liquid phase wetting stage is used to completely melt the solid coal tar pitch powder and fill the microscopic gaps between the lightly oxidized graphite micropowder and the unoxidized spherical graphite particles under the action of capillary force to establish the physical contact basis of the contact interface.

8. The method for preparing a secondary granulation oxidized unoxidized graphite composite coated anode material according to claim 1, characterized in that, The coking value of solid coal tar pitch powder is greater than or equal to 55%, and the content of quinoline insoluble matter present as an impurity in solid coal tar pitch powder is less than or equal to 1.0%; the tap density of unoxidized spherical graphite particles is greater than or equal to 0.95 g / cm³. The preparation method is a completely dry solid-phase treatment process that does not involve the introduction or removal of any liquid solvents, dispersants, or liquid phase binders.

9. The method for preparing a secondary granulation oxidized unoxidized graphite composite coated anode material according to claim 1, characterized in that, Step S3, graphitization, is performed using an Atchison graphitization furnace or an internal series graphitization furnace. The in-situ reduction and graphitization process eliminates the interfacial resistance caused by the introduction of slightly oxidized graphite powder in the precursor mixture, so that the conductivity of the obtained negative electrode material powder is greater than or equal to the conductivity of the control sample without the addition of slightly oxidized graphite powder.

10. The method for preparing a secondary granulation oxidized unoxidized graphite composite coated anode material according to claim 1, characterized in that, After the high-temperature treatment in step S3, the semi-coking studded shell layer in step S2 is transformed into an inlay structure. This inlay structure is characterized by in-situ reduced graphite microcrystals acting as rivet nodes physically interspersed between the base surface of the unoxidized spherical graphite particles and the outer amorphous carbon layer. The inlay structure can suppress the peeling of the coating layer caused by volume expansion during the lithium ion insertion and extraction process of the negative electrode material.

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