Description:FORM 2
THE PATENTS ACT, 1970 (39 of 1970)
&

The Patent Rules, 2003

COMPLETE SPECIFICATION
(See sections 10 & rule 13)
1. TITLE OF THE INVENTION

NEGATIVE ELECTRODE ACTIVE MATERIAL FEATURING GRAPHITIZED CORE AND AMORPHOUS CARBON SHELL DERIVED FROM BIMODAL COKE
2. APPLICANT (S)
NAME NATIONALITY ADDRESS

EPSILON ADVANCED MATERIALS PRIVATE LIMITED

IN
Upadrastha House, 2nd & 3rd Floor, 48, Dr. V. B. Gandhi Marg, Fort, Mumbai
- 400023, Maharashtra, India.
3. PREAMBLE TO THE DESCRIPTION
COMPLETE SPECIFICATION
The following specification particularly describes the invention and the manner in which it is to be performed.

 
FIELD OF THE INVENTION
001 The present invention pertains to negative electrode materials for use in lithium-ion secondary batteries. More specifically, it relates to a novel composite of agglomerated secondary particles derived from bimodal coke comprising isotropic and anisotropic phases. These secondary particles feature a graphitized artificial graphite core and are coated with an amorphous carbon layer, resulting in enhanced electrochemical stability and performance.

BACKGROUND OF THE INVENTION
002 Graphite anode materials significantly influence the performance of lithium-ion batteries. Graphite is considered one of the ideal anode materials due to its ability to reversibly intercalate lithium ions, its low-voltage operational window, and its structurally stable properties. However, improvements in gravimetric and volumetric energy density, fast-charging capability, structural stability, and long cycle life critically depend on the control of particle size distribution, morphology, surface area, and crystallographic orientation are required to further extend the performance of batteries.

003 Anode materials must satisfy competing requirements, including high energy density, rapid charge acceptance, mechanical robustness, and long-term cycling stability. Conventional graphite engineering techniques aim to optimize these properties while minimizing irreversible capacity loss. One widely used approach involves coating graphite particles with amorphous carbon using precursors such as pitch or polymeric materials. While such coatings can suppress parasitic reactions and stabilize the SEI (solid electrolyte interphase), they often lead to high surface area, reduced tap density, non-uniform coatings, and increased irreversible lithium loss, ultimately limiting volumetric energy performance.

004 Another limitation in conventional practice arises from the use of single-phase coke materials, either isotropic or anisotropic, as precursors for synthetic graphite. These materials tend to exhibit non-uniform particle morphology, limited ability to undergo efficient structural transformation into graphite, and inadequate mechanical integrity. Furthermore, their tendency to agglomerate during processing and form inconsistent coatings contributes to reduced performance reliability.

005 Several prior art references reflect ongoing efforts to improve graphite anodes but fail to address these combined limitations. For example, US20240322171A1 discloses graphite anodes with a bimodal particle size distribution and artificial graphite to improve cycle life and fast-charging behavior. However, it does not disclose the use of bimodal coke comprising both isotropic and anisotropic phases, nor does it address core–shell architectures or control over surface area and coating thickness. Similarly, US20220344661A1 discusses amorphous carbon coatings on granulated graphite particles but does not reference bimodal coke, prismatic surface design, or granulation parameters. CN119240684A and US8048339B2 relate to graphite morphology and porous carbon structures, yet neither disclosure addresses the material design and microstructural control necessary to achieve balanced electrochemical properties.

006 Accordingly, there remains a clear technical need for a next-generation graphite anode material that integrates advanced coke selection, morphological control, and surface engineering to overcome the limitations of existing technologies. In particular, the use of bimodal coke—containing both anisotropic and isotropic phases—has emerged as a promising approach to balance structural transformation efficiency during heat treatment, electrical conductivity, and mechanical integrity. When combined with controlled particle morphology and optimized surface characteristics, such materials offer potential advantages in enhancing energy density, fast-charging capability, and long-term cycling performance in lithium-ion battery applications.

OBJECTS OF THE INVENTION
007 The primary object of the present invention is to provide a negative electrode active material comprising agglomerated secondary particles formed from primary particles derived from bimodal coke, the bimodal coke containing both anisotropic and isotropic phases, wherein each secondary particle comprises a carbon core, and an amorphous carbon coating layer acting as a shell is disposed on the surface of the core.

008 Another object of the invention is to utilize a bimodal coke material comprising both isotropic and anisotropic phases in defined weight percentages to achieve a balanced combination of structural stability and conductivity in the electrode material.

009 Yet another object of the invention is to provide a negative electrode active material having a particle size distribution of primary particles, thereby enabling improved packing density and uniform particle morphology.

010 Yet another object of the invention is to provide a method for preparing a negative electrode active material, wherein the secondary particles are subjected to a two-stage heat treatment comprising a first high-temperature treatment to develop a graphitized core, followed by a second carbonization step to form an amorphous carbon coating layer acting as a shell.

SUMMARY OF THE INVENTION
011 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.

012 According to one aspect, the invention provides a negative electrode active material comprising agglomerated secondary particles formed from primary particles derived from bimodal coke. The bimodal coke comprises both anisotropic and isotropic phases in defined weight ratios. The secondary particles include a carbon core, and an amorphous carbon coating layer deposited on the core’s surface, acting as a shell. The bimodal coke further exhibits a particle size distribution with defined D50 ranges for fine and coarse fractions. These attributes contribute to improved tap density and uniform particle packing in the final electrode material.

013 A further aspect of the invention relates to a core-shell configuration of the secondary particles. The core consists of graphitized carbon, while the outer shell comprises an amorphous carbon layer formed by coating the core with a carbon precursor and carbonizing it under controlled conditions. The material is characterized by defined surface area, crystallographic orientation, and particle size ratios that enhance electrochemical performance and lithium-ion retention.

014 In another aspect of the invention provides a method for preparing the negative electrode active material. The method includes crushing the bimodal coke to obtain primary particles, granulating them to form secondary particles, and subjecting the secondary particles to a two-step heat treatment: a high-temperature graphitization step in an inert atmosphere, followed by a lower-temperature carbonization step for forming the amorphous coating layer. By employing bimodal coke with controlled phase content and particle size distribution, and by engineering the resulting core–shell morphology, the invention enables the production of a negative electrode material exhibiting high tap density, structural integrity, and improved performance under high charge-discharge rates. The particles also comprise prismatic planes and dangling bonds that enhance lithium-ion intercalation and structural integrity during cycling.

015 A further aspect of the present invention lies in providing a structurally engineered negative electrode active material suitable for use as an anode in lithium-ion secondary batteries, offering a balanced combination of morphology, thermal stability, and electrochemical performance, while addressing challenges related to material compaction, conductivity, and cycle life.

016 The present invention addresses these limitations through the novel use of bimodal coke, which integrates both anisotropic and isotropic phases along with a particle size distribution. This engineered coke precursor enables the formation of high-tap-density secondary particles with a graphitizable core and uniform carbon coating. The bimodal nature ensures a balance of electrical conductivity and structural stability, while the morphology allows for superior lithium-ion transport and minimal irreversible capacity loss.

017 This, together with the other aspects of the present invention, along with the various features of novelty that characterize 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
018 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:
Fig. 1 illustrates a process flow diagram showing the method steps for preparing the negative electrode active material, including:
Fig. 2 illustrates a metallurgical polished optical micrograph of bimodal coke:
Fig. 3 illustrates a crystallographic orientation comparison using a bar graph or schematic, comparing OI004 index values of the powder form and the electrode form of the graphitized carbon core, as measured by XRD.
Fig. 4 illustrates a Raman spectrum of the negative electrode active material showing ID/IG ratio in the range of 0.1 to 0.3, confirming crystallinity and structural ordering of the graphitized core.
Fig. 5 illustrates tap density vs. particle morphology, possibly a scanning electron microscopy (SEM) image comparison between the primary particles and the spherical or pseudo-spherical secondary particles.
DETAILED DESCRIPTION
019 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.

020 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.

021 Embodiments are provided thoroughly and fully convey the scope of the present disclosure to a person skilled in 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.

022 The terminology used in the present disclosure is only to explain a particular embodiment, and such terminology should 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.

023 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.

024 The term "Bimodal coke" refers to a carbonaceous raw material that contains two distinct particle size populations, typically fine and coarse fractions, and also comprises a mixture of different microstructural phases.

025 The term "Isotropic phase" refers to the microstructure of coke particles that exhibit uniform properties in all directions, usually derived from pitch-based or highly processed carbon sources.

026 The term "Anisotropic phase" refers to coke particles with directional properties due to the ordered crystalline orientation, typically derived from petroleum or needle cokes.

027 The term "Primary particles" refers to the initial fine and coarse particles derived from the crushing of bimodal coke.

028 The term "Secondary particles" refers to agglomerated particles formed by granulating the primary particles, which serve as the base for graphitization and coating processes.

029 The term "Graphitized artificial graphite" refers to the highly ordered crystalline carbon structure obtained by high-temperature treatment of carbonaceous material.

030 The term "Degree of disorder (ID/IG)" is the ratio of D-band to G-band intensities in Raman spectroscopy, indicating the level of defects in the graphite structure. In negative electrode materials, a higher ID/IG ratio suggests more disorder, often seen in secondary particles due to binder-induced surface changes

031 The term "Amorphous carbon coating layer" refers to the disordered carbon material deposited onto the graphite core via carbonization of a carbon precursor.

032 The term "Core-shell structure" refers to a particle morphology in which a central core material, in this case, graphitized artificial graphite, is surrounded by an external shell or coating layer, which in this invention is an amorphous carbon layer, wherein "Core" refers to the inner portion of the secondary particle composed of graphitized artificial graphite that provides conductivity and structural integrity and "Shell" refers to the outer layer of the secondary particle formed by the carbonization of a carbon precursor, which provides interfacial stability and improves lithium-ion intercalation.

033 The term "Tap density" refers to the mass per unit volume of powder after it has been compacted by tapping or vibration, indicating how densely the particles pack together. "TD1000" refers to true density measured using helium pycnometers, which reflects the density of the solid material, excluding open and closed pores.

034 The term "Particle size" in this context refers to the D50 value, which is the median particle diameter at which 50% of the sample's mass consists of smaller particles and 50% consists of larger particles.

035 The term "Agglomeration" refers to the process of clustering smaller primary particles into larger aggregates or secondary particles.

036 The term "Granulating" refers to the mechanical or chemical process of binding primary particles into secondary particles of larger and more controlled dimensions.

037 The term "Predetermined temperature" refers to a specified temperature range chosen for achieving a specific structural transformation, such as graphitization or carbonization, based on material behavior and performance requirements.

038 The term "Oxidation onset temperature" refers in relation to secondary graphite particles, refers to the temperature at which noticeable CO₂ evolution begins during thermal analysis, indicating the start of oxidation. For secondary particles derived from bimodal coke, this typically occurs between 560°C and 600°C due to surface features like dangling bonds and prismatic planes formed during binder mixing.

039 The term” Prismatic planes” in carbon-based materials, particularly in graphite, refers to the non-basal surfaces that are perpendicular to the graphene layer planes. While basal planes are parallel to the graphene layers (002 planes), prismatic planes include planes like (100) and (110), which expose edge sites.

040 The term “dangling bonds” refers to unpaired valence electrons present at the edges or defects of the carbon lattice, particularly where atoms are not fully coordinated due to lattice terminations or structural defects.

041 The term “Volatile matter content” refers to the percentage of components in the coke that are released as gas or vapor when the material is heated to high temperatures in the absence of air. These components include hydrocarbons, tars, water vapor, and other gases that are not part of the fixed carbon or ash content.

042 The term “liquid density” refers to the mass per unit volume of the coke precursor in its liquid phase before coking, typically during the pitch or tar stage, and is usually expressed in g/cm³ at a specified temperature (commonly 25 °C). In the context of bimodal coke used for battery anode materials, it helps assess the quality and carbon yield potential of the feedstock.

043 The term “First-cycle coulombic efficiency” refers to the ratio of the discharge capacity to the charge capacity (lithium inserted during lithiation) during the first cycle of a battery test, typically in a half-cell configuration. It indicates how much irreversible capacity loss occurs in the first cycle, mainly due to SEI formation, electrolyte decomposition, and structural instability.

044 In one embodiment of the invention, the bimodal coke used for forming the primary particles is obtained by subjecting an isotropic pitch to stage thermal treatment across different heating zones under atmospheric pressure. The process involves feeding the isotropic pitch into a container, which is progressively transferred through a series of heating zones operating at increasing temperature ranges. In the initial zone, the pitch is thermally treated at a temperature range of 250°C to 350°C, initiating molecular rearrangement and partial condensation reactions. In the subsequent heating zones, the pitch is exposed to higher temperatures in the range of 350°C to 500°C and then 500°C to 800°C, which promotes advanced carbonization and structural transformation. These thermal stages facilitate the development of a carbon structure containing coexisting isotropic and anisotropic domains, thereby imparting a bimodal microstructure to the resulting coke. Following the completion of thermal treatment across the heating zones, the material is cooled and discharged as bimodal coke. The resulting coke comprises a mixture of anisotropic and isotropic carbon phases, offering a desirable combination of electrical conductivity, mechanical integrity, and compaction characteristics. The obtained bimodal coke is subsequently processed through crushing and classification to produce primary particles, which are then agglomerated to form secondary particles used in the preparation of the negative electrode active material.

045 In another embodiment, the negative electrode active material includes agglomerated secondary particles composed of a plurality of primary particles derived from bimodal coke. The bimodal coke contains both anisotropic and isotropic phases, with the anisotropic phase accounting for approximately 60% to 90% by weight and the isotropic phase comprising about 10% to 40% by weight.

046 In another embodiment the bimodal coke has a volatile matter content (VMC) in the range of 2% to 12% by weight, preferably 5% to 10% by weight and the liquid density in the range of 1.3 g/cc to 2.1 g/cc, preferably 1.4 g/cc to 1.8 g/cc.

047 In one embodiment, the negative electrode active material comprises secondary graphite particles derived from bimodal coke, wherein the particles exhibit a tailored microstructure resulting from binder-induced surface modifications during electrode fabrication. The binder mixing process promotes the formation of surface features, such as dangling bonds and prismatic planes, which enhance binder adhesion, improve the mechanical integrity of the electrode, and facilitate the formation of robust electronic and ionic pathways. These structural characteristics are advantageous for enhancing the overall electrochemical performance, including rate capability and cycle stability. The oxidation onset temperature of the graphite particles was measured using Thermogravimetric Analysis (TGA), wherein approximately 5 mg of the graphite material was heated in a controlled airflow at a linear ramp rate of 10°C/min. The temperature corresponding to the initial evolution of CO₂ was recorded as the oxidation onset temperature. The secondary graphite particles exhibited an onset temperature in the range of about 560°C to 600°C, with a representative mean value of approximately 580°C. In contrast, the primary graphite particles, which lack such surface modifications, exhibited a higher oxidation onset temperature of approximately 670°C, indicating a more ordered and thermally stable graphite lattice. The relatively lower oxidation onset temperature observed for the secondary particles reflects their enhanced surface reactivity and partial structural disorder, which is beneficial in promoting strong binder interaction, enabling efficient electrode processing, and improving long-term electrochemical performance in lithium-ion battery applications.

048 In certain embodiments, the anisotropic phase of the bimodal coke contributes to improved electrical conductivity owing to its highly ordered crystalline structure, while the isotropic phase enhances mechanical strength and offers thermal stability during high-temperature processing.

049 In one embodiment, the selection of bimodal coke is based on its combined advantages of phase composition and particle size distribution, which enhance structural control and energy density for graphite-based anode applications.

050 In another embodiment, the bimodal coke serves as the starting material for forming the core of the negative electrode active material due to its synergistic combination of phase composition and particle size distribution. The bimodal coke is derived from pitch-based carbon sources, and once formed, it is graphitized to serve as the core material. The carbon coating is subsequently applied using an independent carbon precursor to form the amorphous carbon shell.

051 In one embodiment, agglomerated secondary particles of a negative electrode active material are prepared using a bimodal coke comprising both anisotropic and isotropic carbon phases. The bimodal coke is first crushed and milled to produce primary graphite particles with a controlled particle size distribution. These primary particles are dispersed in a medium containing washing oil, which functions as a dispersing aid and surface energy modulator. One or more binders, such as polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC), or styrene-butadiene rubber (SBR), are introduced to promote particle cohesion. The resulting slurry is then subjected to granulation through methods such as spray drying, extrusion, or mechanical agitation, facilitating the agglomeration of primary particles into secondary particles exhibiting spherical or pseudo-spherical morphology. The agglomerated secondary particles are characterized by high tap density, mechanical robustness, and uniform shape, making them suitable for use in high-performance lithium-ion battery electrodes. Optionally, the secondary particles may undergo heat treatment to enhance graphitization or be coated with an amorphous carbon layer to improve surface stability and electrochemical performance.

052 In some embodiments, the primary particles exhibit a D50 in the range of 5 µm to 12 µm, and the resulting secondary particles have a D50 between 13 µm and 22 µm.

053 In one embodiment, the secondary particles undergo a first heat treatment at 2600°C to 3200°C under an inert atmosphere such as argon or nitrogen, transforming their carbon structure into graphitized artificial graphite.

054 In another embodiment, the graphitized secondary particles are coated with a carbon precursor material. This is followed by a second predetermined heat treatment in the range of 900°C to 1400°C, resulting in the formation of an amorphous carbon shell on the surface of the core.

055 In certain embodiments, the resulting core–shell structure includes a graphitized core and an amorphous carbon shell, where the amorphous coating layer is present in an amount of 0.5 wt% to 7 wt% and has a thickness in the range of 10 nm to 100 nm.

056 In some embodiments of the present invention, the carbon precursor is low softening coal tar pitch, petroleum pitch, high softening pitch, zero quinoline insoluble pitch, and a combination thereof.

057 In one embodiment, the surface area of the secondary particles is in the range of 0.8 m²/g to 2.5 m²/g, and the tap density (TD1000) is in the range of 0.9 g/cm³ to 1.5 g/cm³.

058 In another embodiment, the negative electrode active material exhibits a crystallographic orientation index (OI004) corresponding to the (OI004) plane, as determined by X-ray diffraction (XRD) analysis. The orientation index of the (OI004) plane for the powder form of the active material is in the range of 2 to 3. In contrast, when the material is fabricated into a finished electrode, the (OI004) orientation index increases to a range of 8 to 15.

059 In certain embodiments, the granulation process of the primary particles derived from bimodal coke results in agglomerated secondary particles exhibiting a degree of granulation greater than 75%. This indicates that more than 75% of the primary particles are successfully agglomerated into secondary structures, ensuring improved particle uniformity, enhanced tap density, and better processability during electrode fabrication. The high degree of granulation also contributes to improved structural cohesion and packing efficiency within the electrode matrix, thereby supporting enhanced electrochemical performance.

060 In one embodiment, the bimodal coke used for preparing the negative electrode active material exhibits an Oil Absorption Number (OAN) in the range of 40 to 60 mL/100g, as measured by the ASTM D2414 method. The OAN reflects the structural porosity and surface characteristics of the coke particles, indicating their capacity to absorb and retain liquid binder materials during granulation and electrode slurry preparation. A moderate OAN in this range ensures optimal dispersion, binding performance, and mechanical cohesion of the electrode, contributing to improved electrode integrity and long-term cycling stability in lithium-ion battery applications.

061 In another embodiment, the negative electrode active material demonstrates a first discharge capacity in the range of 350 to 358 mAh/g, as measured in half-cell configurations using lithium metal as the counter electrode. This high initial capacity reflects the effective utilization of the active material, optimized particle morphology, and reduced irreversible capacity loss during the first cycle. The capacity achieved is indicative of the material's suitability for high-energy lithium-ion battery applications requiring superior initial performance and minimal formation loss.

062 In some embodiments, the secondary particles exhibit prismatic planes and dangling bonds, enhancing lithium-ion intercalation and cycling stability.

063 In certain embodiments, the Raman ID/IG ratio of the material is in the range of 0.08 to 0.5, and X-ray diffraction (XRD) analysis shows (100) and (110) plane reflections, confirming crystallinity.

064 In one embodiment, the first-cycle coulombic efficiency exceeds 94%, as measured in CR2032-type coin cells using 1M LiPF₆ in EC: DMC as the electrolyte and a charge/discharge current of C/20 between 0.01 V and 1.5 V.

065 In another embodiment, the specific capacity of the active material exceeds 350 mAh/g, with capacity retention of over 85% after 500 cycles, and a rate capability >200 mAh/g at 5C.

066 In some embodiments, post-processing techniques such as milling, surface polishing, or particle classification are applied to ensure a D90/D10 particle size ratio below 3.0, improving uniformity and performance.

067 In one embodiment, the method for preparing the negative electrode active material comprises multiple sequential stages, each contributing to the structural and functional optimization of the final product. Initially, bimodal coke, which contains both anisotropic and isotropic phases, is subjected to a crushing process to obtain primary particles. The crushing is conducted using mechanical impact or attrition milling techniques, ensuring that the resulting primary particles fall within a controlled D50 particle size range, typically between 5 µm and 12 µm. Subsequently, the crushed primary particles are granulated into agglomerated secondary particles. This granulation step may be achieved via spray drying, extrusion, or mechanical agitation to produce spherical or pseudo-spherical morphologies. These morphologies contribute to improved tap density and packing behavior in the final electrode formulation.

068 In another embodiment, the resulting secondary particles are then subjected to a graphitization process under an inert atmosphere, typically argon or nitrogen, at a temperature ranging from 2600°C to 3200°C. This high-temperature treatment facilitates the conversion of disordered carbon structures into crystalline artificial graphite, forming the core of the secondary particles. A controlled heating rate, for instance, 5°C/min, is employed to prevent thermal shock and ensure uniform graphitization throughout the particles.

069 In one embodiment, after graphitization, the surface of the graphitized secondary particles is coated with a carbon precursor material. The coating process may involve solution-based deposition, vapor-phase infiltration, or impregnation techniques.

070 In certain embodiments, the coated particles are subsequently subjected to a carbonization step, in which they are heat-treated at a temperature in the range of 900°C to 1400°C under an inert atmosphere. During this stage, the carbon precursor undergoes pyrolysis, resulting in the formation of an amorphous carbon shell on the surface of the graphitized core. This core–shell structure enhances the material’s electrical conductivity, first-cycle coulombic efficiency, and resistance to side reactions such as solid electrolyte interphase (SEI) formation. The overall process enables the production of a negative electrode active material characterized by high specific capacity, excellent structural integrity, and enhanced performance under fast-charging and high-temperature storage conditions. Optional post-processing steps, such as milling, particle classification, or surface polishing, may also be employed to improve particle uniformity and control the D90/D10 ratio to a value below 3.0.

071 In one embodiment, the secondary particles are porous and spherical, enabling optimized lithium-ion diffusion, mechanical strength, and electrode uniformity.

072 In another embodiment, the amorphous carbon layer improves first-cycle efficiency and SEI layer suppression, contributing to long-term cycling durability in lithium-ion batteries.

073 In some embodiments, the final material is suitable for use in electric vehicles, consumer electronics, and grid-scale energy storage due to its balance of energy density, rate performance, and mechanical stability.

074 In certain embodiments, the present invention provides a negative electrode active material that is suitable for applications requiring both rapid charging capability and long cycle life, while minimizing the loss of cyclable lithium ions during high-temperature storage and operation. The use of bimodal coke as a structural component imparts exceptional properties, owing to its combination of anisotropic and isotropic phases. The anisotropic phase enhances graphitization, thereby contributing to electrical conductivity and structural ordering, whereas the isotropic phase supports mechanical stability and thermal resistance, both of which facilitate extended cycle life. Furthermore, the negative electrode active material comprises artificial graphite exhibiting reduced prismatic planes and lower active surface area, which functions to suppress side reactions between the electrode and electrolyte during storage conditions. As a result, the loss of cyclable lithium ions is significantly reduced, thereby improving the initial coulombic efficiency and capacity retention, particularly under elevated temperature conditions associated with storage and high-rate battery operation.

075 In one embodiment, the bimodal coke comprises fine and coarse particles. Tap density reaches 1.2 to 1.7 g/cm³, while anisotropic and isotropic phases ensure graphitization, conductivity, and thermal stability above 2800°C.

076 In another embodiment, the manufacturing process includes graphitizing the bimodal coke to form primary graphite particles, followed by aggregation into porous, spherical secondary particles. These are subsequently coated with an amorphous carbon layer, deposited to improve first-cycle coulombic efficiency and suppress SEI formation. This embodiment emphasizes the synergistic benefits of combining phase structure, particle distribution, and layered morphology. The resulting material demonstrates a specific capacity >350 mAh/g and first-cycle efficiency >90% in CR2032-type half cells. Owing to its high mechanical strength, reduced porosity, and efficient lithium-ion transport pathways, this electrode material is particularly suited for high-performance lithium-ion batteries, including applications in electric vehicles (EVs) and grid-scale storage systems.

077 Fig. 1 depicts a flow diagram of the method for producing a carbon-coated graphite material obtained from bimodal coke having both isotropic and anisotropic phases. The process begins with raw coke selection (101), wherein bimodal coke possessing dual-phase morphology is chosen to ensure the formation of distinct primary and secondary particles. This is followed by milling (102), which reduces particle size and facilitates the partial liberation of isotropic and anisotropic regions. The milled material then undergoes classification (103), separating particles based on size and morphology, resulting in the isolation of flaky primary particles and spherical or pseudo-spherical secondary particles. The classified particles are subsequently subjected to carbon coating (104), wherein a carbon precursor such as pitch or resin is uniformly applied and thermally treated to form a conductive carbon shell. Thereafter, the carbon-coated particles are exposed to high-temperature graphitization (105), typically above 2500°C, to enhance the crystallinity of the graphite core and convert the coating into a graphitic structure. Finally, post-treatment and packaging (106) are performed to ensure particle size uniformity and readiness for application as a negative electrode active material in lithium-ion batteries.

078 Fig. 2 illustrates an optical micrograph of bimodal coke obtained through metallurgical polishing and microscopic examination. The image provides visual evidence of the microstructural characteristics of the coke, revealing the presence of both anisotropic and isotropic domains. The anisotropic regions appear to be flow-textured, layered structures, whereas the isotropic regions exhibit a more uniform and featureless morphology. This micrograph serves as an illustrative example supporting the structural duality of the bimodal coke, which contributes to its unique electrochemical and mechanical properties when used as a precursor for the negative electrode active material.

079 Fig. 3 illustrates the X-ray diffraction (XRD) pattern of artificial graphite, highlighting its crystallographic orientation through distinct diffraction peaks. The dominant peak at approximately 26.5° (2θ) corresponds to the (002) plane, which is indicative of well-developed graphitic layers and high crystallinity. Additional peaks at higher angles, specifically the (004) and (110) planes, further confirm the structural ordering of the graphite material. This XRD pattern is used to calculate the Orientation Index (OI₀₀₄), which reflects the degree of preferred orientation in the c-axis direction. The OI₀₀₄ value, derived from the relative intensity of the (004) and (002) peaks, is a critical parameter for evaluating the structural anisotropy and alignment of the graphite crystals. Ref-3 supports the structural characterization of the graphitized carbon core used in the invention, and can be used comparatively to demonstrate differences between the powder form and the electrode form of the same material. Higher OI₀₀₄ values in the electrode form, for instance, reflect enhanced alignment achieved during the electrode fabrication process.

080 Fig. 4 illustrates a Raman spectrum of the negative electrode active material, highlighting its structural features and degree of graphitization. The spectrum exhibits three characteristic peaks: the D-band near 1350 cm⁻¹, the G-band around 1580 cm⁻¹, and the 2D-band at approximately 2700 cm⁻¹. The G-band corresponds to the E₂g phonon mode of sp²-hybridized carbon atoms, indicating graphitic ordering within the carbon lattice. The D-band, associated with structural defects or disordered carbon, arises from breathing modes of sp² carbon rings. The 2D-band, a second-order overtone of the D-band, further supports the presence of layered graphitic structures. The intensity ratio I_D/I_G is observed to be in the range of 0.1 to 0.3, signifying a high degree of crystallinity and low defect density in the graphitized carbon core. This low ratio confirms that the material predominantly comprises well-ordered graphitic domains with minimal amorphous content, which is desirable for high-performance lithium-ion battery anode materials. This serves as analytical validation for the structural integrity and quality of the graphitized carbon core within the negative electrode active material.

081 Fig. 5a and Fig. 5b present scanning electron microscopy (SEM) images illustrating the difference in particle morphology between primary particles and agglomerated secondary particles, respectively. These morphological characteristics directly influence the tap density of the negative electrode active material, which is a critical parameter for electrode compaction and volumetric energy density in lithium-ion batteries. Fig. 5a shows the microstructure of crushed primary particles, which are irregular in shape, sharp-edged, and show a wide particle size distribution. The particles appear loosely packed, leading to relatively lower tap density due to interstitial voids and inefficient packing behavior. In contrast, fig. 5b illustrates the morphology of agglomerated secondary particles, which exhibit a spherical or pseudo-spherical form with a more cohesive and ordered structure. These secondary particles are composed of primary particles bonded together, often through mechanical or thermal granulation processes. The spherical morphology promotes better flowability and enables higher packing density, resulting in improved tap density of the electrode material. This comparison highlights the functional advantage of controlled particle engineering in improving the bulk properties of the negative electrode active material.

EXAMPLES
082 Example 1: Properties of bimodal coke for negative electrode material preparation
In this example, bimodal coke was prepared from coal tar pitch by subjecting it to a thermal treatment at temperatures ranging from 550°C to 800°C under atmospheric conditions. The resulting coke exhibited a dual-phase structure composed predominantly of anisotropic domains, along with a minor isotropic fraction. The key physical properties of the prepared bimodal coke are summarized in the table below.
Table-1
Property Value
Composition 85% Anisotropic, 15% Isotropic
Volatile Matter Content 3 – 5%
Moisture Content <1%
Liquid Density >1.4 g/cc
Heat Treatment Temperature 550 – 800°C

083 Example 2: Properties of bimodal coke for electrode material preparation
In this example, bimodal coke was prepared by thermally treating coal tar pitch at temperatures ranging from 470°C to 550°C under atmospheric conditions. This controlled thermal process resulted in a dual-phase carbon structure consisting of both anisotropic and isotropic domains. The physical characteristics of the resulting bimodal coke are presented in the table below:
Table-2
Property Value
Composition 75% Anisotropic, 25% Isotropic
Volatile Matter Content >9%
Moisture Content <1%
Liquid Density >1.4 g/cc
Heat Treatment Temperature 470 – 550°C

084 Example 3: Preparation of negative electrode material from bimodal coke
Example illustrates: This example outlines the complete process of fabricating the negative electrode active material using a bimodal coke system. The selected coke, featuring both anisotropic and isotropic phases, undergoes granulation to form uniform secondary particles. These are then subjected to high-temperature graphitization to develop a crystalline graphite core. A carbon precursor is subsequently applied and carbonized to produce an amorphous carbon shell. This core–shell structure enhances both electrical conductivity and interface stability, contributing to high specific capacity and prolonged cycle life. To prepare a negative electrode material using bimodal coke with controlled dual-phase content.
• Bimodal coke: 75% anisotropic, 25% isotropic
• Fine particles D50 = 3 µm, Coarse particles D50 = 15 µm
• Granulation by spray drying
• Graphitization: 2800°C (argon atmosphere)
• Coating: 5 wt% petroleum pitch, carbonized at 1200°C
Table-3
Property Value
D50 13 – 18 µm
TD1000 0.9 – 1.2 g/cc
Surface area Max. 0.8 – 2.5 m2/g
OI (004) powder 2 – 5
OI (004) Electrode 8 - 20
First Discharge Capacity 345 – 358 mAh/g
FCE ≥ 94%
Amorphous Shell C coating 1 – 8%
Degree of granulation >75%
OAN 25 - 60

085 Example 4: Preparation of negative electrode material from single-phase coke and its comparison with bimodal coke
Example illustrates: This comparative study evaluates the performance difference between a conventional single-phase anisotropic coke and the invented bimodal coke-based material. The bimodal configuration enables a balance of structural reinforcement and electrical conductivity due to the integrated phase diversity, resulting in superior tap density, higher initial coulombic efficiency, and better long-term electrochemical performance. Compare the electrochemical performance of single-phase vs. bimodal coke.
• Sample A: 100% anisotropic coke
• Sample B: Bimodal coke (65% anisotropic, 35% isotropic)
Parameter Sample A (Single-Phase) Sample B (Bimodal)
Tap Density (g/cm³) 1.2 1.1
First-Cycle Efficiency (%) 93 92.0
Specific Capacity (mAh/g) 355 350
Cycle Retention (500 cycles) 78% 86%
Table-4

086 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
087 The technical advantages offered by the present invention are as follows:
088 The present invention provides full automation of the coke handling process, from pitch charging to final packaging, significantly reducing manual intervention and enhancing operational efficiency.
089 The present invention enhances electrochemical performance by utilizing a unique bimodal coke comprising both anisotropic and isotropic phases, offering both cyclic stability and quick charge capabilities
090 The present invention provides a structurally optimized core–shell architecture, wherein the core is graphitized artificial graphite, and the shell is amorphous carbon, resulting in superior lithium-ion intercalation and stable SEI formation.
091 The present invention improves tap density and particle packing through size distribution, ensuring better electrode compaction and mechanical cohesion.
092 The present invention enhances thermal and structural integrity due to the presence of isotropic phase coke, enabling high-temperature stability during processing and cycling.
093 The present invention provides improved electrical conductivity and graphitization via the anisotropic phase, which contributes to a highly ordered graphite core formation at high temperatures (2600–3200°C).
094 The present invention enhances first-cycle coulombic efficiency, achieving values exceeding 94%, thereby reducing irreversible capacity loss and improving initial battery performance.
095 The present invention provides high specific capacity, delivering values >350 mAh/g, which supports high energy density applications such as EVs and grid storage.
096 The present invention enhances morphological control, with secondary particles granulated to achieve >75% granulation efficiency and spherical or pseudo-spherical shape, improving processability and uniformity.
097 The present invention provides a controlled carbon coating thickness ensuring uniform surface protection and stable SEI formation without impeding lithium transport and Li- plating
098 The present invention enhances electrode mechanical stability, supported by controlled OAN and TD density, ensuring long-term cycling and volumetric density without structural degradation.
099 The present invention improves crystallographic orientation, achieving an OI004 index of 8–15 in electrodes, which boosts the quick charge capability and structural alignment.
100 The present invention provides compatibility with high-performance battery requirements, making it suitable for EVs, consumer electronics, and grid-scale energy storage due to its balanced energy density, thermal performance, and mechanical robustness.
101 The present invention improves electrode slurry formation and binder dispersion, due to the high porosity and surface structure of bimodal coke particles.
102 The present invention enhances capacity retention and lithium inventory, by suppressing lithium loss at elevated storage temperatures and minimizing irreversible surface reactions.
103 The present invention provides a comprehensive solution to limitations in existing graphite-based anodes by integrating structure, morphology, and functional enhancements through precise material and process engineering.
 
, Claims:1. A negative electrode active material comprising agglomerated secondary particles, wherein:
a) the secondary particles are formed from primary particles derived from a bimodal coke comprising both anisotropic and isotropic phases;
b) the secondary particles comprise a graphite core; and
c) an amorphous carbon coating layer is disposed on the surface of the graphite core.

2. The negative electrode active material as claimed in claim 1,
wherein the amorphous carbon coating layer is formed from a carbon precursor selected from low and high softening point coal tar pitch, petroleum pitch, zero quinoline-insoluble pitch, and combinations thereof.

3. The negative electrode active material as claimed in claim 1, wherein the bimodal coke comprises 60% to 90% by weight of anisotropic phase and 10% to 40% by weight of isotropic phase.

4. The negative electrode active material as claimed in claim 1, wherein the bimodal coke particle distributions comprise a dual particle nature of isotropic and anisotropic phases.

5. The negative electrode active material as claimed in claim 1, wherein the bimodal coke has an Oil Absorption Number (OAN) in the range of 20 to 60 mL/100g.

6. The negative electrode active material as claimed in claim 1, wherein the graphite core has a crystallographic orientation index (OI004) in the range of 2 to 4 in powder form and 8 to 20 in electrode form, as determined by X-ray diffraction (XRD).

7. The negative electrode active material as claimed in claim 1, wherein the agglomerated secondary particles have a D90/D10 particle size ratio less than 3.0.

8. The negative electrode active material as claimed in claim 1, wherein the bimodal coke has a volatile matter content (VMC) in the range of 2% to 12% by weight.

9. The negative electrode active material as claimed in claim 1, wherein the bimodal coke has a liquid density in the range of 1.3 g/cc to 2.1 g/cc.

10. The negative electrode active material as claimed in claim 1, wherein the secondary particles comprise prismatic planes and dangling bonds.

11. The negative electrode active material as claimed in claim 10, wherein the secondary particles are characterized by an oxidation onset temperature in the range of 550°C to 590°C, as determined by thermogravimetric analysis under an oxidative atmosphere.

12. The negative electrode active material as claimed in claim 1, wherein the primary particles have a D50 particle size in the range of 5 µm to 12 µm, and the secondary particles comprise a core of artificial graphite having a D50 particle size in the range of 13 µm to 22 µm.

13. The negative electrode active material as claimed in claim 1, wherein the amorphous carbon coating is in the range of 0.5 wt% to 7 wt% based on the total weight of the negative electrode active material.

14. The negative electrode active material as claimed in claim 13, wherein the electrode active material has a degree of disorder (ID/IG) in the range of 0.08 to 0.5.

15. A method for preparing a negative electrode active material, the method comprising:
a) crushing a bimodal coke material comprising both anisotropic and isotropic phases to obtain a plurality of primary particles;
b) granulating the primary particles to form agglomerated secondary particles;
c) subjecting the agglomerated secondary particles to a first predetermined heat treatment under an inert atmosphere to form a graphite core;
d) applying a carbon precursor material onto the surface of the graphite core to obtain coated particles; and
e) subjecting the coated particles to a second heat treatment to carbonize the precursor and form an amorphous carbon coating layer.

16. The method as claimed in claim 15, wherein the secondary particles comprise prismatic planes and dangling bonds.

17. The method as claimed in claim 15, wherein the carbon precursor is selected from low softening point coal tar pitch, petroleum pitch, high softening point pitch, zero quinoline-insoluble pitch, and combinations thereof.

18. The method as claimed in Claim 15, wherein the first predetermined heat treatment for graphitization is carried out at a temperature in the range of about 2600°C to about 3200°C.

19. The method as claimed in Claim 15, wherein the second predetermined heat treatment for carbonization is carried out at a temperature in a range from about 900° C. to about 1400° C.

20. The method as claimed in Claim 15, wherein the primary particles have a D50 particle size in the range of 5 µm to 12 µm, and the secondary particles comprise a core of artificial graphite having a D50 particle size in the range of 13 µm to 22 µm.