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

Abstract

A crucial step in the production of battery grade natural graphite for lithium-ion batteries is the spheroidization process. However, the spheroidization yield is typically only about 50%. The by-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 petroleum pitch coating that allows for revalorization and recycling of waste graphite from the spheroidization process. Re-agglomeration of graphite fines was achieved by spray drying technique using 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 petroleum pitch for simultaneous binder and pitch decomposition to obtain pitch-coated particles. Resulting agglomerate particles showed a median size 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 stability in comparison with non-coated graphite agglomerate. The electrochemical performance of the coated material was comparable to a commercial graphite reference, particularly in terms of cumulative irreversible capacity. Analysis by X-ray nano-computed tomography provided further insight into morphological properties and dimensional changes after calendering 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 lithium-ion batteries.