Description:FIELD OF THE INVENTION
001 The present invention relates to a method for making uniform amorphous carbon-coated graphite composite for quick charge applications and low irreversibility.

BACKGROUND OF THE INVENTION
002 Lithium-ion batteries (LIBs) are central to advancing energy storage technologies for electric mobility and renewable energy systems. The anode material, a critical component of LIBs, must balance high energy density, power, quick charging, structural stability, and long-cycle life. It is always best to apply optimal engineering practices when synthesizing graphite anode materials to enhance properties such as low irreversibility, long cycle life, and fast charging capabilities.

003 To overcome these limitations, prior art has focused on enhancing graphite anodes by coating them with amorphous carbon precursors (e.g., pitch, polymers, or biomass-derived carbon). Such coating aims to improve lithium-ion diffusion, suppress electrolyte decomposition, and buffer volume changes during cycling. Despite these efforts, conventional coating methods face unresolved challenges. Excessive surface area in the amorphous carbon layer accelerates parasitic reactions with the electrolyte, leading to unstable solid-electrolyte interphase (SEI) formation, irreversible lithium loss, and rapid capacity fade. Additionally, non-uniform coating thickness and particle agglomeration during synthesis reduce tap density, resulting in low volumetric energy density. This necessitates thicker electrodes, increasing cell weight and impairing ion transport efficiency.

004 A critical yet overlooked challenge lies in the uncontrolled presence of trace oxygen or steam during carbon precursor decomposition. Excessive oxygen oxidizes the carbon matrix, while insufficient functional groups (e.g., carboxyl or hydroxyl) weaken binder adhesion, causing mechanical degradation and delamination during cycling. Furthermore, inconsistent residence time during pyrolysis leads to incomplete precursor conversion or over-graphitization, disrupting the balance between the amorphous carbon’s buffering capacity and electrical conductivity. These issues collectively result in poor packing efficiency, uneven slurry dispersion, and reduced cycle stability, limiting scalability and commercial viability.

005 Existing solutions, such as doping additives or multi-step coating processes, often address isolated parameters (e.g., surface area or particle size) while neglecting the interdependence of synthesis variables like oxygen content, residence time, and thermal gradients. For instance, mechanical milling to refine particle size distribution may inadvertently increase surface area, exacerbating SEI growth. Similarly, inert-atmosphere pyrolysis eliminates functional groups essential for binder interaction, compromising electrode integrity.

006 To address these challenges, inventors precisely regulate trace oxygen and steam levels, optimizing loading density and residence time for controlled carbonization and ensuring uniform and homogeneous coating engineering. The invention achieves a tailored carbon microstructure with minimized surface reactivity, enhanced tap density, and robust mechanical adhesion. This approach resolves the trade-offs between electrochemical performance and manufacturability, enabling thinner, high-capacity electrodes with improved cycle life and safety. The process is scalable, cost-effective, and suitable for diverse climatic conditions, aligning with the demand for high-performance energy storage solutions.

OBJECTS OF THE INVENTION
007 The objective of the present invention is to provide method for producing an uniform amorphous carbon-coated graphite composite material, the method comprising mixing graphite particles with a carbon precursor to form a mixture; heating the mixture at a first predetermined temperature in an inert atmosphere to obtain a calcined mixture; and carbonizing the mixture at a second predetermined temperature for a predetermined residence time to form an amorphous carbon layer on surfaces of the graphite particles. During carbonization, the calcined mixture was heated in the presence of an inert atmosphere under a predetermined ppm level of oxygen. The calcined mixture is carbonized at a loading density in the rage of 0.65 g/cm³ to 0.79 g/cm³, which is suitable for forming a uniform amorphous carbon layer on the surfaces of the graphite particles

SUMMARY OF THE INVENTION
008 This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description section. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to determine the scope of the claimed subject matter. The difficulties and drawbacks of previous approaches are addressed in the present invention.

009 An aspect of the present invention discloses a method for graphite anode material core with amorphous carbon coating shell and optimizing their surface area through controlled thermal treatment parameters, including material loading density and residence time. The process involves two primary stages: (1) mixing graphite, carbonaceous precursor and heating the mixture at a first predetermined temperature in an inert atmosphere to obtain a calcined mixture (2) carbonizing the calcined mixture at a second predetermined temperature for a predetermined residence time in an inert atmosphere containing oxygen at a predetermined parts per million (ppm) level to form an amorphous carbon layer on the surfaces of the graphite particles, thereby obtaining the carbon-coated graphite composite material.

010 Another aspect of the invention provides a method wherein graphite particles are combined with a carbon precursor. The mixture is heated to a temperature between 200°C and 600°C under an inert atmosphere, initiating calcination. This results in the decomposition of the precursor and the formation of a uniform amorphous carbon coating on the graphite surface.

011 Yet another aspect of the invention lies in the carbonizing stage, conducted at 700°C to 1300°C, where material loading density is precisely controlled. At a loading density of approximately 0.65g/cm3 to 0.79g/cm3, the process ensures uniform particle proximity, enabling efficient and uniform desorption of volatile matter from the surface of coated graphite particles. Lower densities (~0.5 g/cm3) or loosely packed materials allow faster desorption kinetics, which in turn avoid the volatile vapor deposition upon the graphite particles. This avoids contamination by soot, which would otherwise reduce the active surface area of the material. However, overly low densities risk incomplete carbonization due to insufficient particle interactions. Conversely, higher densities (~0.9 g/cm3) slow desorption kinetics, increasing volatile vapor redeposition as soot particles. While this contamination elevates the active surface area due to the porous nature of soot, it compromises material purity. During carbonization, the calcined mixture was heated in the presence of an inert atmosphere under a predetermined ppm level of oxygen in the inert atmosphere in the range of 50 ppm to 1300 ppm. The calcined mixture is carbonized at a loading density in the rage of 0.65 g/cm³ to 0.79 g/cm³, which is suitable for forming a uniform amorphous carbon layer on the surfaces of the graphite particles.

012 A further aspect of the invention employs a staged loading process during carbonization, wherein material is incrementally introduced into the furnace to maintain the optimal loading density. Residence time is adjusted: shorter durations at elevated temperatures minimize volatile matter contamination upon graphite particles.

013 Another aspect of the invention relates to the resultant uniform composite material, which exhibits a tailored surface area, rendering it highly suitable for applications such as lithium-ion battery anodes, supercapacitors, and catalytic supports. The invention addresses prior limitations in carbon-coated graphite synthesis by irreversible loss, long life cycle, and safe operation.

014 This, together with the other aspects of the present invention, along with the various features of novelty that characterized the present disclosure, is pointed out with particularity in the claims annexed hereto and forms a part of the present invention. For a better understanding of the present disclosure, its operating advantages, and the specified objective attained by its uses, reference should be made to the accompanying descriptive matter in which there are illustrated exemplary embodiments of the present invention.

DESCRIPTION OF THE DRAWINGS
015 The advantages and features of the present invention will become better understood with reference to the following detailed description taken in conjunction with the accompanying drawings:

016 Fig.1 Flow diagram for the method for preparing uniform carbon-coated graphite composite material.

017 Figure 2 illustrates a graph showing the specific surface area across different temperature zones, from the calcination mixture to the carbonization stage.
DETAILED DESCRIPTION
018 The exemplary embodiments described herein detail for illustrative purposes are subjected to many variations. It should be emphasized, however, that the present invention is not limited to a negative material electrode and its method of preparation as disclosed. It is understood that various omissions and substitutions of equivalents are contemplated as circumstances may suggest or render expedient, but these are intended to cover the application or implementation without departing from the spirit or scope of the present invention.

019 Unless otherwise specified, the terms used in the specification and claims have the meanings commonly used in the field of negative electrode material and the method of preparation involved therein. Specifically, the following terms have the meanings indicated below.

020 Embodiments are provided thoroughly and fully convey the scope of the present disclosure to the person skilled in the art. Numerous details are set forth relating to specific components and methods to provide a complete understanding of the embodiments of the present disclosure. It will be apparent to the person skilled in the art that the details provided in the embodiments should not be construed to limit the scope of the present disclosure. In some embodiments, known processes, well-known apparatus or structures, and well-known techniques are not described in detail.

021 The terminology used in the present disclosure is only to explain a particular embodiment, and such terminology shall not be considered to limit the scope of the present disclosure. As used in the present disclosure, the forms "a,” "an," and "the" may be intended to include the plural forms as well unless the context suggests otherwise. The terms "comprises," "comprising," “including,” and “having,” are open-ended transitional phrases and therefore specify the presence of stated features, integers, steps, operations, elements, modules, units, and/or components, but do not forbid the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The order of steps disclosed in the method and process of the present disclosure is not to be construed as necessarily requiring their performance as described or illustrated. It is also to be understood that additional or alternative steps may be employed.

022 As used herein, “combinations thereof” is inclusive of one or more of the recited elements, optionally together with a like element not recited, e.g., inclusive of a combination of one or more of the named components, optionally with one or more other components not specifically named that have essentially the same function. As used herein, the term “combination” is inclusive of blends, mixtures, alloys, reaction products, and the like.

023 The term “loading density” refers to the amount of a material (like graphite or amorphous carbon) packed into a given volume or area, often expressed as mass per unit area (e.g., mg/cm²) or mass per unit volume (e.g., g/cm³). In other terms, it’s about how much active material is "loaded" onto an electrode surface or within a structure, impacting performance metrics like capacity, conductivity, and stability.

024 The term “Surface area (BET)” refers to the total surface area of the graphite particles as measured by the Brunauer-Emmett-Teller (BET) method, typically expressed in square meters per gram (m²/g).

025 The term “Tap density” refers to the mass of the graphite powder per unit volume after it has been tapped or compacted, typically measured in grams per cubic centimeter (g/cm³), and is an indicator of how tightly the particles pack together.

026 The term “Calcination” refers to the heating of graphite and amorphous carbon to a high temperature (e.g., 200°C-600°C) in a controlled atmosphere to remove volatile impurities, moisture, or organic components and potentially modify their structure or properties without melting them.

027 The term 'carbonization' refers, in the context of amorphous carbon and graphite, to the thermal process of heating organic or carbon-containing materials to a high temperature (typically 700°C to 1300°C or higher) in an oxygen-limited or inert atmosphere (e.g., nitrogen or argon), converting them into a carbon-rich residue by driving off non-carbon elements like hydrogen, oxygen, and volatile compounds.

028 The term 'desorption kinetics' refers, in this context, to the rate at which adsorbed substances are released from the ordered layers of graphite or the porous, disordered structure of amorphous carbon, influenced by factors such as temperature, surface area, and material-specific interactions.

029 The term "Capacity of an electrode" refers to the amount of electrical charge (measured in milliampere hours, mAh or Ah/kg) that an electrode can store and deliver per unit mass of its active material, essentially defining how much electricity the electrode can hold based on its weight; it is often expressed as "specific capacity" to indicate the capacity per gram of the electrode material. It is typically measured in mAh/g or Ah/kg (milliampere hours per gram).

030 The term “ribbon blender” refers to a mixing device that homogeneously combines graphite and amorphous carbon using a double-helical ribbon agitator in a U-shaped trough, ensuring uniform particle dispersion for applications such as battery electrode preparation.

031 The term (wt%) refers to weight percentage and is the mass of a component in a mixture expressed as a percentage of the total mass of the mixture. It is used to represent the concentration of a substance in a mixture based on its weight relative to the overall weight.

032 The term “First cycle efficiency" of an electrode refers to the ratio of the discharge capacity during the very first charge-discharge cycle of a battery to the charge capacity during that same cycle, essentially indicating how much of the initial charge is effectively stored and can be later retrieved during the first discharge, often used in the context of lithium-ion batteries where a significant portion of the initial charge can be lost due to irreversible side reactions during the first cycle.

033 The term “Oxygen concentration” in ppm refers to the amount of oxygen present in the environment, measured in parts per million, which is crucial in controlling the oxidation during the preparation of graphite-coated carbon or carbon-coated graphite. Maintaining low oxygen concentration levels (in ppm) is essential to prevent unwanted oxidation and ensure the quality of the coating process

034 The term “negative electrode” here refers to the anode material used in a lithium battery, which is typically made of a carbonaceous material such as graphite, silicon, or combinations thereof. It absorbs lithium ions from the electrolyte during the charging process.

035 The present invention provides a method for producing high-purity, artificial graphite uniform, carbon-coated composite material uniformly and optimized for negative electrode materials in lithium-ion batteries. The process integrates precise control of loading density, residence time, temperature profiles, and material composition to achieve efficient carbonization, uniform heat transfer, and minimal contamination (e.g., soot or re-condensed volatiles). The method addresses limitations in conventional processes by dynamically balancing these parameters, ensuring high surface area and electrochemical performance.

036 In an embodiment of the present invention, a graphitization process is carried out by placing carbonaceous material into a high-temperature furnace. The furnace is heated to above 2300 degrees Celsius under an inert argon atmosphere, and the temperature is maintained for 4 to 8 hours to facilitate the crystallographic alignment of the carbon structure. After the desired time, the graphitized material is gradually cooled to room temperature. The resulting artificial graphite exhibits enhanced crystallinity, making it suitable for applications requiring high electrical conductivity and thermal stability.

037 In an embodiment of the present invention, carbonaceous material is bulk mesophase (BMC) coke, needle coke, fluid coke, flexicoke, pitch coke, asphalt coke, green coke, pet coke, gas coke, synthetic coke, or combinations thereof.

038 In an embodiment of the present invention, artificial graphite is first mixed with a carbon precursor in a ribbon blender mixer and calcination takes place from 2000C to 6000C where the surface area increases when temperature increases and heating at stage wise heating there after carbonization takes place from 7000C to 13000C step wise heating at residence time with a proper loading density. During this process, an optimal loading density is maintained, which ensures uniform proximity between the carbon-coated graphite particles. This uniformity promotes consistent heat transfer and efficient desorption of volatile matter. During carbonization, the calcined mixture was heated in the presence of an inert atmosphere under a predetermined ppm level of oxygen in the inert atmosphere in the range of 50 ppm to 1300 ppm. The calcined mixture is carbonized at a loading density in the rage of 0.65 g/cm³ to 0.79 g/cm³, which is suitable for forming a uniform amorphous carbon layer on the surfaces of the graphite particles.

039 In another embodiment of the present invention, a method for synthesizing uniform carbon-coated graphite particles uniformly with optimized electrochemical performance comprises: preparing a composite of artificial graphite and a carbon precursor; compacting the composite into a tubular furnace at a controlled loading density within the range of 0.3 g/cm³ to 0.99 g/cm³; and carbonizing the compacted material under an inert atmosphere at 700°C to 1300°C for about 4 to 6 hours. Critical to the invention is the identification of an optimal loading density range of 0.65–0.79 g/cm³, wherein enhanced particle proximity promotes uniform heat transfer and efficient desorption of volatile matter during carbonization, thereby suppressing re-deposition and maximizing surface area. Deviations from this range—such as densities exceeding 0.80 g/cm³, which reduce void space and impede volatile escape, or suboptimal densities below 0.5 g/cm³, which degrade carbonization efficiency due to insufficient particle contact—result in diminished surface areas (<10 m²/g) and compromised electrochemical function. By synergizing the optimized density with precise thermal parameters (temperature and residence time), the method yields a carbon material exhibiting accelerated ion diffusion kinetics, enhanced charge storage capacity, and improved graphitization of the carbon coating, as demonstrated in lithium-ion battery negative electrodes. This novel integration of controlled density, thermal regulation, and structural outcomes, validated through comparative experimentation, resolves limitations inherent to conventional carbonization processes and establishes a scalable industrial framework for high-performance negative electrode material.

040 In an embodiment of the present invention, the relationship between residence time and loading density is critical to achieving efficient carbonization while minimizing contamination. Optimal loading density (~0.6 to 0.75 g/cm³) ensures uniform particle proximity, which promotes consistent heat transfer and volatile matter desorption. Deviations from this density range disrupt kinetics: Higher densities (e.g., ~0.9 g/cm³) reduce desorption rates, prolonging volatile retention and enabling re-condensation as soot, while lower densities (~0.5 g/cm³) risk incomplete carbonization due to insufficient thermal coupling between particles. Residence time must be carefully calibrated to complement these density effects. Shorter durations at high temperatures (e.g., 700°C-1300°C for about 4 to 6 hours) limit volatile re-deposition by rapidly evacuating vapors before they adhere to particle surfaces. Conversely, prolonged exposure to lower densities exacerbates soot formation as volatiles linger in the furnace atmosphere. Industry studies emphasize that fixed residence times—without dynamic adjustment for temperature and density—often result in trade-offs between carbonization efficiency and contamination control. For instance, loosely packed materials subjected to extended heating exhibit higher soot content, whereas densely packed batches with insufficient residence time retain unprocessed volatiles. By integrating staged loading (to maintain optimal density) with adaptive residence time modulation, the invention addresses a key gap in conventional processes, which often prioritize one parameter at the expense of the other. This dual optimization ensures both rapid desorption kinetics and minimal soot contamination, achieving a balance critical for high-purity, high-surface-area graphite production.
041 In an embodiment of the present invention to achieve a uniform coating on graphite, coating experiments were conducted in a vertical mixer furnace with continuous stirring maintained at 5–30 RPM under an inert nitrogen atmosphere within a temperature range of 200°C to 600°C. Following this, the coated graphite underwent static heating for carbonization at a predetermined temperature and residence time. During the carbonization process, volatile matter was evaporated, resulting in the formation of an amorphous carbon coating on the graphite. The resulting surface properties, including surface area, were influenced by the material's loading density during carbonization and its oxygen content.

042 In an embodiment of the present invention, the carbon-coated graphite composite material has a specific surface area (BET) ranging from 0.8 m²/g to 5.5 m²/g and a tap density of 0.80 g/cm³ to 1.55 g/cm³.

043 In an embodiment of the present invention, the carbon-coated graphite composite material includes 90 wt% to 99 wt% artificial graphite and 1 wt% to 10 wt% carbon precursors, based on the total weight percentage of the carbon-coated graphite composite material.

044 In an embodiment of the present invention, the carbon-coated graphite composite material includes 90 wt% to 99 wt%, preferably 90 wt% to 96 wt%, and preferably 92 wt% to 96 wt% of artificial graphite.

045 In an embodiment of the present invention, the carbon-coated graphite composite material includes 1 wt% to 10 wt%, preferably 2 wt% to 10 wt%, preferably 5 wt% to 10 wt% of carbon precursors.

046 In another embodiment of the present invention, the carbon precursor is low softening coal tar pitch, petroleum pitch, high softening pitch, zero quinoline insoluble pitch, compounds, aliphatic hydrocarbons, naphthalene, cyclic hydrocarbons, and other oxygen-nitrogen compounds, or a combination thereof.

047 In an embodiment of the present invention, the coal tar pitch may have a coking value in a range from about 40 percent to about 80 percent. In another embodiment of the present invention, the coal tar pitch may have a coking value in a range from about 45% to about 55%.

048 In an embodiment of the present invention, the coal tar pitch may have a viscosity in a range from about 1 centipoise to about 10 centipoises in a temperature range from about 70 degrees centigrade to about 100 degrees centigrade. In another embodiment of the present invention, the coal tar pitch may have a coking value in a range from about 3 centipoises to about 5 centipoises in a temperature range from about 70 degrees centigrade to about 100 degrees centigrade.

049 In an embodiment, the present invention relates to a method for the preparation of a uniform carbon-coated graphite composite comprising the following steps:

050 Preparation of Graphite and Carbon Precursor:
Graphite particles are mixed with a carbon precursor selected from coal tar, pitch, polymers, and hydrocarbons. The precursor and graphite mixture are heated in an inert atmosphere (e.g., nitrogen or argon) to initiate pyrolysis. The temperature range for this step is between 200°C and 600°C. During calcination, the precursor decomposes, forming an amorphous carbon layer on the surface of the graphite particles. The material undergoes carbonization at a temperature between 700°C and 1300°C, where the material’s loading density plays a critical role in the outcome. At low densities ~0.5 g/cm³, gas flow and heat distribution are optimal, but the carbonization may be incomplete due to inadequate particle interaction. At high densities ~0.9 g/cm³, the particles are tightly packed, which restricts gas diffusion, reduces surface area, and promotes particle fusion. The optimal loading density for carbonization is around 0.7 g/cm³, which ensures both uniform heat transfer and sufficient precursor decomposition without causing particle clustering.

051 Staged Loading Method:
To achieve the optimal loading density, a staged loading method is employed, where material is incrementally added during carbonization. The process begins with a lower initial loading density ~0.5 g/cm³ to allow precursor decomposition and early-stage carbonization. Gradual additions are made to reach the optimal density ~0.7 g/cm³ as the temperature rises, optimizing particle interactions and gas flow at each stage. During carbonization, the calcined mixture was heated in the presence of an inert atmosphere under a predetermined ppm level of oxygen in the inert atmosphere in the range of 50 ppm to 1300 ppm

052 Residence Time:
The residence time is about 0.830C/min with a carbonization temperature of 700°C to 1300°C for about 4 to 5 hours. These parameters allow for an isolated assessment of loading density’s impact on the material’s final properties, which are critical for applications such as negative electrodes in electrochemical devices.

053 Final Composite:
The surface area of resulting uniform graphite coated with amorphous carbon is highly optimized, making it suitable for high-performance negative electrode material.

054 In one embodiment of the present invention, the method for producing a uniform carbon-coated graphite composite involves a two-stage thermal process to optimize loading density and surface area, both critical for high-performance battery anodes. During calcination (200°C to 600°C), the carbon precursor (e.g., pitch) decomposes, volatilizing components and forming a porous, disordered pre-carbon layer on the graphite, temporarily increasing the surface area from 1–3 m²/g to 10–15 m²/g. In the subsequent carbonization stage (700–1300°C). This reduces the final surface area to a controlled 0.8–3.5 m²/g while achieving an optimal loading density (0.65–0.79 g/cm³). The controlled surface area minimizes electrolyte decomposition (enhancing cycle life) and increases the lithium-ion diffusion pathways for rapid charge/discharge.

055 In one embodiment of the present invention, amorphous carbon is utilized as a carbon precursor for the preparation of a uniform composite material. The incorporation of amorphous carbon leverages its inherently disordered and porous structure, characterized by a larger d-spacing compared to crystalline carbon, to enhance the electrochemical properties of the resulting electrode. During the fabrication process, the amorphous carbon-containing mixture is subjected to a calcination stage, wherein the precursor is uniformly integrated into the electrode matrix, benefiting from its high surface area and accessibility. Subsequently, a carbonization step is applied, during which the amorphous carbon undergoes a structural transition from a disordered to a more ordered state under controlled thermal conditions. This transformation enhances the structural integrity and electrochemical performance of the negative electrode material, while the initial large d-spacing of the amorphous carbon facilitates rapid ion diffusion and intercalation, outperforming crystalline carbon in terms of ionic transport efficiency. The negative electrode material of this embodiment, incorporating amorphous carbon as a precursor, exhibits improved fast-charging capabilities and charge-discharge efficiency. These advantages arise from the optimized ion pathways and enhanced surface interactions provided by the amorphous carbon, which, even after partial ordering during carbonization, retains superior accessibility compared to fully crystalline alternatives. Thus, this embodiment illustrates the effective use of amorphous carbon as a carbon precursor in a mixed negative electrode material, delivering enhanced performance in applications requiring high-rate charge storage and release.

056 Referring to Fig. 2, the graph illustrates the calcination temperature vs specific surface area provides the method for preparing uniform amorphous carbon-coated graphite composite for a negative electrode, the surface area increases during the calcination stage (200°C to 600°C) because the carbon precursor (e.g., pitch) decomposes and volatilizes, forming a porous, disordered pre-carbon layer on the graphite, boosting the surface area from the graphite’s initial low value (e.g., 1–2 m²/g) to a higher range (e.g., 10–15 m²/g); however, it decreases during the carbonization stage (700°C to 1300°C) as the higher temperatures cause the porous layer to densify, collapse pores, and sinter into a smoother, compact amorphous carbon coating, reducing the surface area to a controlled optimal range (e.g., 0.8–3.5 m²/g), which balances electrochemical performance by minimizing side reactions while maintaining sufficient lithium intercalation capacity for battery applications.

EXAMPLES

057 Example 1: Method for preparing uniform carbon-coated graphite with a loading density of 0.5 g/cm³
A negative electrode material is prepared by blending a composition comprising 94 wt% artificial graphite and 6 wt% coal tar pitch (as a carbon precursor) in a ribbon blender to form a homogeneous mixture. The mixture is calcined at 200°C to 600°C for 3 to 4 hours under an inert atmosphere to eliminate residual volatiles and stabilize the precursor structure. Subsequently, the calcined material is compacted into a tubular furnace at a controlled loading density of 0.5 g/cm³ and carbonized at a temperature gradient ranging from 700°C to 1300°C for 4–5 hours, with a slow heating rate of 0.83°C/min during the ramp phase under 15 ppm of oxygen, as evidenced by the resultant carbon-coated graphite material exhibiting 99.95% purity, a surface area of 2 m²/g (measured via BET analysis), and soot content of around 0.5%.
058 Example 2: Method for preparing uniform carbon-coated graphite with a loading density of 0.7 g/cm³.
In one illustrative example, a negative electrode material is prepared by blending a composition comprising 94 wt% artificial graphite and 6 wt% coal tar pitch (as a carbon precursor), in a ribbon blender to form a homogeneous mixture. The mixture is calcined at 200°C to 600°C for 3 to 4 hours under an inert atmosphere to eliminate residual volatiles and stabilize the precursor structure. Subsequently, the calcined material is compacted into a tubular furnace at a controlled loading density of 0.7 g/cm³ and carbonized at a temperature gradient ranging from 700°C to 1300°C for 4–5 hours, with a slow heating rate of 0.83°C/min under 70 ppm of oxygen during the ramp phase. This optimized thermal profile, combined with the defined loading density, facilitates efficient volatile desorption while minimizing re-deposition, as evidenced by the resultant carbon-coated graphite material exhibiting 99.5% purity, a surface area of 6 m²/g (measured via BET analysis), and soot content below 0.1%.

059 Example 3: Method for preparing uniform carbon-coated graphite with a loading density of 0.9 g/cm³.
In one illustrative example, a negative electrode material is prepared by blending a composition comprising 94 wt% artificial graphite and 3 wt% coal tar pitch (as a carbon precursor) in a ribbon blender to form a homogeneous mixture. The mixture is calcined at 200°C to 600°C for 3 to 4 hours under an inert atmosphere to eliminate residual volatiles and stabilize the precursor structure. Subsequently, the calcined material is compacted into a tubular furnace at a controlled loading density of 0.7 g/cm³ and carbonized at a temperature gradient ranging from 700°C to 1300°C for 4–5 hours, with a heating rate of 0.83°C/min under 30 ppm of oxygen during the ramp phase, as evidenced by the resultant carbon-coated graphite material exhibiting 99.95% purity, a surface area of 10 m²/g (measured via BET analysis), and soot content above 1.5%.
060 Example 4: Method for preparing uniform carbon-coated graphite with a loading density of 0.7 g/cm³.
In one illustrative example, the negative electrode is comprised of 96 wt.% of artificial graphite and 4 wt.% of coal tar pitch in a ribbon blender to form a uniform coating at 200 – 600 ℃ for 3-4 hours under an inert nitrogen atmosphere. The coated mixture is further loaded into carbonization ranging from 700 – 1300 ℃ for 4–5 hours, with a heating rate of 0.83 ℃/min under 1300 ppm of oxygen. The resultant material has a surface area of 12.5 m2/g with a purity of 99.3 %.
061 Example 5: Method for preparing uniform carbon-coated graphite with a loading density of 0.7 g/cm³.
In one illustrative example, the negative electrode is comprised of 96 wt.% of artificial graphite and 4 wt.% of coal tar pitch in a ribbon blender to form a uniform coating at 200℃ to 600℃ for 3-4 hours under an inert nitrogen atmosphere. The coated mixture is further loaded into carbonization ranging from 700 – 1300 ℃ for 4–5 hours, with a heating rate of 0.83 ℃/min under 700 ppm of oxygen. The resultant material has a surface area of 8.5 m2/g with a purity of 99.5 %
062 Example 6: Method for preparing uniform carbon-coated graphite with a loading density of 0.7 g/cm³.
In one illustrative example, the negative electrode is comprised of 96 wt.% of artificial graphite and 4 wt.% of coal tar pitch in a ribbon blender to form a uniform coating at 200 – 600 ℃ for 3-4 hours under an inert nitrogen atmosphere. The coated mixture is further loaded into carbonization ranging from 700 – 1300 ℃ for 4–5 hours, with a heating rate of 0.83 ℃/min under 110 ppm of oxygen. The resultant material has a surface area of 5.3 m2/g with a purity of 99.95 %
TABLES
063 Table 1: Effect of surface area across calcination and carbonization temperatures
Different heat treatment temperatures Surface area
4000C 1.181667
5000C 1.813
6000C 3.372
7000C 13.225
8000C 5.673
10000C 7.054333
11000C 3.603
13000C 2.147
16000C 1.93

064 The experimental results are summarized as follows: at 400°C, the surface area was measured at 1.18 m²/g, indicating minimal volatile removal and limited pore development at this lower temperature. Increasing the temperature to 500°C yielded a surface area of 1.81 m²/g, suggesting the onset of enhanced volatile release. At 600°C, the surface area rose to 3.37 m²/g, and a significant increase to 13.23 m²/g was observed at 700°C, likely due to optimal volatile desorption and pore formation. However, beyond this peak, the surface area decreased to 5.67 m²/g at 800°C, possibly due to the onset of structural consolidation or pore collapse. Further increases to 1000°C and 1100°C resulted in surface areas of 7.05 m²/g and 3.60 m²/g, respectively, indicating a stabilization followed by a decline as higher temperatures promoted greater ordering of the carbon structure. At 1300°C and 1600°C, the surface areas were 2.15 m²/g and 1.93 m²/g, respectively, reflecting a trend toward reduced porosity as the material approached a more graphitic, ordered state. These findings demonstrate that the heat treatment temperature critically influences the surface area, with an optimal range around 700°C maximizing porosity and surface area, which are advantageous for electrochemical applications requiring high ion accessibility. The inventors’ study highlights the importance of tailoring the temperature profile to achieve the desired material properties, balancing surface area with structural integrity. This temperature-dependent behavior, coupled with the specific composition of graphite, carbon precursor, underscores a key aspect of the invention’s versatility and optimization potential.

065 Table 2: Comparative Studies-Effect of surface area due to slow and fast heating with controlled residence time
Sample Description Density g/c3 Surface area Residence time
Slow heating – 7000C (500C/hr); LB with press & with lid 0.7 to 0.95 10.762 0.830C/min
Slow heating - 7000C (500C/hr); SB without press & with lid
(Loosely) 0.3 to 0.65 2.937 0.830C/min
Fast heating - 7000C (2500C/hr); LB with press & with lid 0.7 to 0.95 5.341 4.20C/min
Fast heating - 7000C (2500C/hr); SB without press & with lid (Loosely) 0.3 to 0.65 1.685 4.20C/min

066 In a comparative study of carbon-coated graphite synthesis, samples processed in a tubular furnace under slow heating (700°C/hr, 0.83°C/min) with pressing (0.7–0.95 g/cm³) and a lid achieved a surface area of 10.76 m²/g, demonstrating optimal volatile desorption and pore formation due to uniform heat transfer and particle proximity. In contrast, loosely packed samples (0.3–0.65 g/cm³) under identical slow heating exhibited significantly lower surface area (2.94 m²/g), highlighting the detrimental effects of insufficient particle contact. Fast heating (2500°C/hr, 4.20°C/min) further degraded performance, reducing surface areas to 5.34 m²/g (pressed) and 1.69 m²/g (unpressed), as rapid temperature ramps disrupted volatile removal and induced pore collapse. These results underscore the criticality of combining slow heating (0.83°C/min), high loading density (0.7–0.95 g/cm³), and lid usage to maximize surface area and structural integrity, with the pressed, slow-heated configuration emerging as the optimal embodiment for high-performance electrodes, balancing efficient carbonization, minimal soot formation, and superior electrochemical properties.
067 Table 3: Comparative studies calculation of loading densities for carbon-coated graphite in tubular furnace configurations.
Tubular Furnace Loading Densities
Sl.no Name Loaded Mass (in g) Loaded Volume (in CC) Loaded Density (In g/CC) Remarks
1 Large Boat 157 184.56 0.851 Pressed material
2 Small Boat 70 143.17 0.489 Not Pressed material

068 Table 3 presents the calculated loading densities of carbon-coated graphite samples processed in a tubular furnace, comparing the effects of pressing versus not pressing the material. The table includes two samples: one loaded into a large boat with pressed material, and another loaded into a small boat with unpressed material. Loading density, defined as the mass of the material per unit volume (expressed in g/cm³), is a critical parameter influencing heat transfer, volatile desorption, and the final properties of the carbon-coated graphite, such as purity and surface area.

069 For the first sample (Serial No. 1, Large Boat), a mass of 157 grams of carbon-coated graphite was pressed into a volume of 184.56 cm³, yielding a loading density of 0.851 g/cm³. The pressing process compacts the material, reducing inter-particle voids and increasing the density, which enhances particle proximity and uniformity during heat treatment. This higher density is advantageous for efficient heat distribution and volatile matter escape, as observed in subsequent carbonization steps.

070 In contrast, the second sample (Serial No. 2, Small Boat) consisted of 70 grams of carbon-coated graphite loaded into a volume of 143.17 cm³ without pressing, resulting in a loading density of 0.489 g/cm³. The absence of pressing leaves the material in a loose, less compact state, leading to a lower density. This reduced density may result in less uniform heat transfer and incomplete volatile removal due to greater inter-particle spacing, potentially affecting the material’s final properties, such as increased soot content or reduced surface area.

071 The data in Table 3 illustrates the impact of pressing on loading density, with the pressed sample achieving a density approximately 74% higher (0.851 g/cm³ vs. 0.489 g/cm³) than the unpressed sample. These differences underscore the importance of controlling loading density in the tubular furnace to optimize the processing of carbon-coated graphite. The pressed material’s higher density aligns with findings that densities above 0.75 g/cm³ enhance volatile desorption and surface area development, while lower densities, such as 0.489 g/cm³, may lead to suboptimal outcomes. This comparison provides a basis for tailoring the preparation method to achieve the desired material characteristics, a key feature of the present invention.

Table 4: Comparative Studies-Effect of loading density on material purity and soot content

Loading Density (g/cm³) Residence Time (min) Temperature (°C) Purity (%) Soot Content (%)
0.5 0.830C/min 1100 96.0 0.5
0.7 0.830C/min 1100 99.5 <0.1
0.9 0.830C/min 1100 97.0 1.5

072 Table 4 summarizes the results of comparative studies conducted to evaluate the influence of loading density on the purity and soot content of a carbon-based material, such as carbon-coated graphite, during processing in a tubular furnace. Three distinct loading densities—0.5 g/cm³, 0.7 g/cm³, and 0.9 g/cm³—were tested under consistent conditions of 0.830C/min residence time and a carbonization temperature of 1100°C. These parameters allow for an isolated assessment of loading density’s impact on the material’s final properties, which are critical for applications such as negative electrodes in electrochemical devices.

073 At a loading density of 0.5 g/cm³, the material achieved a purity of 96.0% with a soot content of 0.5%. This lower density, indicative of a less compact arrangement of particles, suggests reduced particle proximity, which may limit uniform heat transfer and volatile desorption efficiency during carbonization. Consequently, while the soot content remains moderate, the purity is lower than optimal, reflecting incomplete removal of impurities or volatile matter due to insufficient densification.

074 In contrast, at a loading density of 0.7 g/cm³, the material exhibited a significantly higher purity of 99.5% and a soot content of less than 0.1%. This loading density represents an optimal balance, where the particles are sufficiently close to ensure efficient heat distribution and rapid volatile escape, minimizing re-deposition and soot formation. The high purity and near-negligible soot content indicate that this density enhances the structural integrity and cleanliness of the carbon material, making it highly desirable for high-performance applications requiring minimal impurities.

075 However, when the loading density increased to 0.9 g/cm³, the purity dropped to 97.0%, and the soot content rose sharply to 1.5%. This higher density, while still facilitating heat transfer, appears to overly compact the material, potentially restricting pathways for volatile matter to escape. As a result, trapped volatiles may decompose and form soot, reducing the material’s purity and increasing undesirable residues. This trend suggests that, beyond an optimal threshold, excessive densification counteracts the benefits observed at 0.7 g/cm³. The data in this table demonstrates that loading density plays a pivotal role in determining the purity and soot content of the processed material, with 0.7 g/cm³ emerging as the most effective value under the specified conditions of 0.830C/min at 1100°C. The observed variations—ranging from 96.0% to 99.5% purity and 0.5% to less than 0.1% soot content at lower and optimal densities, respectively, versus a decline at higher density—highlight the need for precise control of loading density to optimize material quality. These findings underscore a key aspect of the present invention, wherein the method of preparing carbon-based materials achieves superior outcomes by tailoring loading density to balance volatile desorption and structural purity, as evidenced by the minimal soot content and high purity at 0.7 g/cm³.

076 Table-5 Comparison of Oxygen Concentration and Surface Area for Coated Carbon-Graphite Composite Materials
Name Oxygen concentration (ppm) Surface area (m2/g)
Large Boat 1 1000 – 1500 11 - 18
Large Boat 2 300 - 900 4-10
Large Boat 3 50-300 1.5-2.8

077 The table compares the oxygen concentration and surface area of three large boat samples of coated carbon-graphite composite materials. Large Boat 1 has the highest oxygen concentration (1000–1500 ppm) and the largest surface area (11–18 m²/g), indicating significant exposure to oxygen and a higher reactivity. Large Boat 2 has a moderate oxygen concentration (300–900 ppm) and a smaller surface area (4–10 m²/g). In contrast, Large Boat 3 exhibits the lowest oxygen concentration (50–300 ppm) and the smallest surface area (1.5–2.8 m²/g), suggesting reduced oxidation and lower reactivity. This indicates a general trend where higher oxygen concentrations are associated with larger surface areas and vice versa

078 While the foregoing describes various embodiments of the disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof. The invention is not limited to the described embodiments, versions, or examples, which are included to enable a person having ordinary skill in the art to make and use the invention when combined with information and knowledge available to the person having ordinary skill in the art.

ADVANTAGES OF THE INVENTION
079 The technical advantages offered by the present invention are as follows:
080 The present invention provides uniform particle packing and reduces electrode heterogeneity, resulting in improved consistency and performance of the electrode material.
081 The present invention enhances tap density, enabling greater material compaction and higher volumetric efficiency.
082 The present invention achieves an optimal loading density with controlled surface area and particle size distribution, optimizing electrochemical properties and processing efficiency.
083 The present invention improves the mechanical integrity of the negative electrode material, enhancing durability and structural stability during use.
084 The present invention provides that surface area plays a significant role in determining oxygen concentration, with loading density having a secondary influence
 
, Claims:1. A method for producing a uniform amorphous carbon-coated graphite composite material, the method comprising:
(a) mixing graphite particles and a carbon precursor to form a mixture;
(b) calcining the mixture at a first predetermined temperature in an inert atmosphere to obtain a calcined mixture; and
(c) carbonizing the calcined mixture at a second predetermined temperature for a predetermined residence time in an inert atmosphere containing oxygen at a predetermined parts per million (ppm) level to form an amorphous carbon layer on the surfaces of the graphite particles, thereby obtaining the uniform amorphous carbon-coated graphite composite material.

2. The method as claimed in claim 1, wherein the carbon precursor is selected from the group consisting of low softening and high softening coal tar pitch, petroleum pitch, high softening pitch, zero quinoline insoluble pitch, and a combination thereof.

3. The method as claimed in claim 1, wherein the first predetermined temperature is in the range of 2000C to 6500C, preferably in the range of 3000C to 6000C.

4. The method as claimed in claim 1, wherein the second predetermined temperature is in the range of 7000C to 13000C, preferably in the range of 10700C to 12000C.

5. The method as claimed in claim 1, wherein the predetermined residence time is 4 to 6 hours at a heating rate of 0.5°C/min to 1.0°C/min.

6. The method as claimed in claim 1, wherein the calcined mixture is carbonized at a loading density that is suitable for forming a uniform amorphous carbon layer on the surfaces of the graphite particles.

7. The method as claimed in claim 6, wherein the loading density is in the rage of 0.65 g/cm³ to 0.79 g/cm³.

8. The method as claimed in claim 1, wherein the carbon-coated graphite composite material has a tap density of 0.80 g/cm³ to 1.50 g/cm³.

9. The method as claimed in claim 1, wherein the carbon-coated graphite composite material has a surface area in the range of 0.5 m²/g to 5.5 m²/g.

10. The method as claimed in claim 1, wherein the predetermined parts per million (ppm) level of oxygen in the inert atmosphere is in the range of 50 ppm to 1300 ppm.