NH ₄ F Electrolyte Enhanced Natural Graphite Electrolysis Purification and Lithium Battery Anode Application

Muscovite and quartz are the main impurities that control the purity of natural graphite. They appear as layered and particulate phases inside the carbon layers or on the graphite surfaces. These forms lengthen diffusion paths during treatment and increase HF consumption. We designed an electrochemical purification system that uses NH4F and H2SO4 as the electrolyte to avoid direct contact of toxic HF. First, hydrochloric acid pretreatment was used to remove Fe, Ca, Mg, and other elements that form insoluble fluorides with HF. The pretreated graphite was pressed into pellets and used as the anode. Electrolysis was carried out at 3 V in an electrolyte of 1.0 M NH4F and 25 wt % H2SO4. This increased fixed-carbon purity from 97.72% to 99.9% with a yield of 90%. The results show that the NH4F–H2SO4 electrochemical method removes the need for direct HF contact and significantly improves the purification efficiency. When the purified graphite was used as an anode in lithium batteries and cycled 400 times at 0.2 C, it retained 84.5% of its initial capacity. This study offers an efficient and more sustainable route for graphite purification and supports the development of natural graphite as a lithium battery anode material.