Mechanistic insights into the solvent assisted thermal regeneration of spent graphite and its upcycling into dual graphite batteries†
Abstract
Industrial focus on lithium-ion battery (LIB) recycling is mainly limited to revenue-generating cathode materials, while the graphite anode is often overlooked as its deficit is not alarming yet. Herein, a sequential segregation method is applied to recover and reprocess trapped Li inside the anode as synthetic-grade Li2CO3, whereas the extracted graphite is treated by a solvent assisted thermal method to prepare for second-life applications. The mechanisms behind the evolution of structural properties and surface chemistries during the typical steps of solvent assisted thermal treatment using three chemically dissimilar solvents, i.e., H2O, DMC, and HCl are elucidated. Utilizing H2O as a solvent is the most benign option, but the electrochemistry obtained from H2O-treated graphite is not up to the mark. Organic solvent DMC tunes the interfacial chemistry in such a way that it benefits second-life electrochemistry. Inorganic acid HCl produces the highest carbon purity with an almost impurity-free surface, making it suitable for non-electrochemical applications too. The electrochemical superiority of DMC-treated graphite is maneuvered to fabricate a dual-graphite full cell that functions on a scissor-cutting ion-storage mechanism, yielding 4.5 V vs. Li+/Li output voltage and 90.3 W h kgcell−1 of energy density at 91% efficiency and retaining 77% energy over 500 cycles.