From waste graphite fines to revalorized anode material for Li-ion batteries

Overview & Synopsis

More than 50% of natural graphite material is wasted during the spheroidization process in the production of battery grade graphite for lithium-ion batteries. The waste product consists of graphite fines that are not suitable for use in lithium-ion batteries due to their small particle size (<10 µm), therefore, graphite fines are discarded or sold at a loss. In this work, we report a method for graphite fines re-agglomeration and coal tar pitch coating that allows for revalorization and recycling of waste graphite from the spheroidization process. Reagglomeration of graphite fines was achieved by spray drying technique with the use of carboxymethyl cellulose as binder and citric acid as cross-linking agent to improve the mechanical strength of the agglomerate. The as-obtained particles were subjected to heat treatment in presence of coal tar pitch for simultaneous binder and pitch decomposition to obtain pitch-coated particles. Resulting agglomerate particles showed D50 comparable to a commercial battery grade natural graphite reference and proved structurally sound to withstand the electrode calendering process. Pitch-coated agglomerate particles exhibited lower surface area and improved cycling stability with respect to non-coated agglomerate particles, as well as half-cell electrochemical performance comparable to a commercial graphite reference, particularly in terms of cumulative irreversible capacity. Analysis by nano-computed tomography provided further insight into morphological properties and dimensional changes after calendaring and upon galvanostatic cycling. Overall, the material obtained through this method shows great potential for re-introduction in the production chain of battery grade natural graphite for lithiumion batteries.