Application of chlorination technology for the conversion of natural flake graphite into coated spherical purified graphite for Li-ion batteries

• Demonstrates a scalable HF-free purification route to battery-grade natural graphite • Integrates chlorination into a full CSPG production process • Achieves ultra-high purity while preserving graphite structure • Final product matches or exceeds commercial anode performance The growing demand for lithium-ion batteries (LiBs) has intensified the need for high-purity graphite anodes. Natural flake graphite (NFG) offers a cost-effective and environmentally favorable alternative to synthetic graphite but requires extensive purification to meet battery-grade standards. This study investigates the integration of chlorination-based purification into the conversion of NFG into coated spherical purified graphite (CSPG) suitable for LiB applications. The process combines caustic leaching, high-temperature chlorination, micronization-spheroidization, and pitch-based carbon coating. Material characterization reveals that carbochlorination effectively removes refractory impurities, achieving ultra-high purity (>99.95 wt.% C) without compromising graphite crystallinity. Morphological analysis shows that micronization-spheroidization yields highly circular particles with optimized tap density and particle size distribution. The final carbon coating step induces a marked decrease in the specific surface area of the powder below 3 m 2 g -1 , as desired. The final CSPG exhibits electrochemical performance comparable to a commercial reference (BTR918) in coin half-cell configuration, with a reversible capacity of 365 mAh g -1 and an initial coulombic efficiency of 92%. Its long-term cycling performance in NMC811/graphite pouch cell is remarkable, displaying a capacity retention of 88.2% after 1500 cycles compared to 85.3% with the commercial reference. This study confirms the relevance of carbochlorination purification for commercial LiB anode production. This HF-free approach offers a scalable and environmentally sustainable alternative to conventional purification methods.