Complete Natural Graphite Anode Material Production Process

Natural Graphite Anode Material Production Process Overview

Unveiling the Mystery of Natural Graphite Anode Materials

To understand the importance of natural graphite anode materials, we first need to comprehend how lithium-ion batteries work. In lithium-ion batteries, the cathode and anode are like two “parking lots,” while lithium ions are the “vehicles” shuttling back and forth between these parking lots. When the battery charges, lithium ions “move” from the cathode to the anode; during discharge, they return from the anode to the cathode.

Natural graphite anode material plays the role of this “parking lot.” Its unique layered structure provides an ideal storage space for lithium ions, with a working potential range of 50-200 mV vs Li/Li+. What’s even more remarkable is that this process is completely reversible, which is the key to lithium-ion batteries’ ability to repeatedly charge and discharge.

Compared to synthetic graphite, natural graphite possesses inherent advantages. Due to its perfect crystal structure formed over geological ages, natural graphite exhibits higher crystallinity, superior electrical conductivity, and thermal conductivity. From a cost perspective, natural graphite’s raw material costs are significantly lower than synthetic graphite, which requires high-temperature synthesis, giving it substantial competitive advantages in large-scale commercial applications.

Technical Challenges Facing Raw Graphite and Process Development

However, the raw graphite bestowed upon us by nature is not perfect. Graphite directly mined from deposits faces numerous technical challenges when used as battery anode material. The most prominent issue is graphite’s anisotropy—natural graphite has a typical flaky structure, layered like pages in a book. While this structure provides excellent conductivity in certain directions, it performs poorly in the perpendicular direction.

Another challenging problem is the irregularity of particle shapes. Raw flaky graphite leads to low packing density, affecting battery volumetric energy density; sharp edges can easily puncture separators, creating safety hazards; additionally, flaky particles have poor dispersibility in electrode slurries, affecting electrode uniformity.

To address these technical challenges, after decades of technological development and process optimization, modern natural graphite anode material production has evolved into a complete and precise step process flow. This process design philosophy is “gradual progression, pursuing excellence”—starting with initial crushing, progressively removing impurities, optimizing shape, and increasing purity to ultimately obtain spherical graphite particles with ideal performance characteristics.

Complete Production Process Flow Details

Crushing – The First Step of a Long Journey

Graphite ore extracted from mines typically exists in large chunks that need to be crushed to a suitable size range of 10-30mm to lay the foundation for subsequent precision processing. Although the crushing process may seem simple, it bears the important mission of optimizing raw material conditions for the entire production line.

Considering that graphite hardness is typically medium hardness (Mohs hardness 1-2), the crushing process is relatively simple, commonly employing three-stage open circuit, two-stage open circuit, or single-stage open circuit processes. For equipment selection, jaw crushers are commonly used for coarse crushing of large minerals, while hammer crushers and impact crushers are used for secondary crushing. Precise control of operating parameters is crucial, with crushing ratios generally controlled at 3-5:1, ensuring both crushing efficiency while avoiding energy waste and subsequent processing difficulties.

Flotation – The First Step in Separating the Wheat from the Chaff

The flotation process fully utilizes the fundamental differences in surface properties between graphite and other minerals. Graphite possesses natural hydrophobicity, like water droplets on lotus leaves, easily combining with bubbles and floating to the water surface; while impurity minerals like quartz and feldspar are hydrophilic, tending to remain in water.

To enhance separation effectiveness, carefully proportioned flotation reagents are required. Common collectors include kerosene, diesel oil, heavy oil, and other non-polar hydrocarbon oils, typically used at 200-500g/t. Frothers commonly use pine oil, at 20-50g/t. pH adjusters like lime adjust slurry pH to 8-9. Optimized flotation processes can improve graphite purity from approximately 20% in raw ore to 84-85%, with high-quality flotation achieving 80-95%, while maintaining recovery rates above 90%.

Grinding – Precise Particle Size Control

The grinding process aims to achieve precise and uniform particle size distribution, which is crucial for subsequent spheroidization processes. Target particle size D50 is precisely controlled at 15-25μm, a range determined based on extensive experimental data as optimal for spheroidization processing.

Rod mills are used to achieve the required grinding while minimizing graphite particle size reduction. Grinding density should be uniformly maintained at above 65% solids content. To rapidly select large flake graphite, the grinding stage commonly employs multi-stage grinding processes combined with flotation for separation. Modern classifier mills have become industry mainstream choices due to their excellent particle size control capabilities, with the unique advantage of performing precision classification simultaneously with grinding, ensuring high uniformity in product particle size distribution.

Spheroidization – The Core Process of Shape Revolution

Spheroidization is the core step of the entire process flow, achieving the crucial transformation from flaky to spherical shape. In specially designed spheroidization equipment, graphite particles undergo continuous and precisely controlled collision, friction, and shear forces, with flakes gradually curling and folding to ultimately form approximately spherical three-dimensional structures.

Modern spheroidization processes typically control processing time at 15-30 minutes, a time window optimized through extensive experimentation as the optimal balance point. The performance improvements from spheroidization are revolutionary: spheroidization can increase particle specific surface area by 1.8 times, providing more active sites for lithium-ion intercalation and deintercalation; spherical structures significantly increase tap density, thereby improving battery volumetric energy density.

Traditional spheroidization processes face the major challenge of low yield, with spheroidization yields typically only 30-50%. NETZSCH’s GyRho spheroidization system employs revolutionary design concepts, optimizing airflow patterns and particle motion trajectories to improve yields to above 80%, a technological breakthrough that establishes a solid foundation for large-scale industrial production.

Shaping – The Final Touch for Perfection

The shaping process further refines and optimizes spheroidization results. Although graphite particles after spheroidization treatment already basically present spherical shapes, there is still room for improvement in shape regularity and surface smoothness. Shaping processes use relatively gentle yet precise mechanical forces to remove residual sharp edges from particle surfaces, further improving surface smoothness and sphericity.

Compared to spheroidization, shaping uses much gentler processing forces and relatively shorter processing times (5-15 minutes), primarily for fine-tuning rather than drastically changing basic particle shapes. Modern equipment can achieve spherical graphite tap density of 963 g/l with D50 values of 16.8μm. After shaping, particle sphericity should reach above 0.9, with significantly reduced surface roughness—improvements that have important practical value for increasing electrode compaction density and reducing side reactions with electrolytes.

Purification – Chemical Refinement for Ultimate Purity

Although graphite purity after flotation reaches 95-98%, battery-grade applications require even stricter purity standards. Chemical purification processes employ precisely controlled acid leaching, using hydrofluoric acid (HF), hydrochloric acid (HCl), and nitric acid (HNO3) for multiple treatments.

According to authoritative research data, optimal leaching conditions are 20% HCl + 4% HF acid type and concentration, 85°C leaching temperature, and 4-hour leaching time. Another study shows that using 1.0 N HCl at 80°C for 5 minutes can achieve maximum carbon content of approximately 97%.

Through acid-alkali-acid (H2SO4/H2O2-NaOH-HCl) chemical purification processes, carbon content can be significantly improved from 94.71% to 99.68%. With additional HF leaching, carbon content can reach 99.72%, fully meeting strict battery-grade application requirements.

Coating Granulation – Dressing Graphite in Protective Armor

Coating granulation processes dress pure spherical graphite particles in a “protective coat,” addressing the issue of graphite surface active sites easily undergoing side reactions with electrolytes. Using high softening point pitch (HSP pitch) or phenolic resin as coating materials, advanced technologies like fluidized beds or spray drying form uniform coating layers of 2-5nm thickness on particle surfaces.

Precise control of coating layer thickness is crucial: too thin cannot provide sufficient protective effects, while too thick increases lithium-ion transport resistance, affecting battery rate performance. Modern coating equipment optimizes airflow distribution and spray patterns to achieve above 95% coating uniformity, ensuring each particle receives ideal protection.

High-temperature Carbonization – The Magnificent Transformation of Coating Layers

High-temperature carbonization processes transform organic coating materials into stable carbon protective layers. Under strictly controlled high-temperature environments of 900-1200°C, precise carbonization treatment is performed under inert atmosphere (nitrogen or argon) protection, with organic coating materials gradually decomposing and rearranging to form stable amorphous carbon structures.

Temperature control is the technical key to this process. Too low temperatures prevent complete carbonization of organic materials, with residual components potentially decomposing to produce gas during battery use; too high temperatures may damage graphite crystal structures. Adopting precise control strategies of staged heating ensures complete carbonization reactions while protecting graphite’s excellent properties.

Demagnetization – Eliminating Potential Safety Hazards

Demagnetization processes use strong magnetic fields (>1T) to thoroughly remove magnetic impurities from products, primarily iron and its compounds. Although these magnetic materials have very low content, they may trigger unexpected safety issues during long-term battery use, requiring thorough removal through professional magnetic separation equipment.

Modern demagnetization equipment employs permanent magnet or electromagnetic technologies to effectively identify and separate various magnetic impurities, ensuring magnetic material content in demagnetized products is controlled below 50ppm, providing reliable safety assurance for stable battery operation.

Screening – Final Precision Particle Size Control

Screening processes are the final checkpoint for product quality control, using precise air classification technology to accurately control product particle size to the ideal range of D50 16-20μm. This precise particle size control not only ensures product consistency but also provides stable and reliable raw materials for customers’ subsequent electrode preparation processes.

Advanced air classification equipment can achieve extremely precise particle size cutting, controlling particle size distribution span within 2.0 and classification efficiency above 85%, ensuring final products fully meet customers’ strict requirements.

Packing Systems – The Final Line of Quality Defense

Final packaging processes use moisture-proof, anti-static professional packaging materials and automated packaging systems to ensure product quality stability during storage and transportation. Modern packaging lines are equipped with precision weighing, filling, and sealing equipment, not only improving packaging efficiency but also ensuring ±0.5% packaging accuracy.

Strict environmental controls ensure product moisture content below 0.5%, with professional packaging materials effectively preventing external moisture intrusion, providing customers with consistently high-quality products.