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 kg_cell⁻¹ of energy density at 91% efficiency and retaining 77% energy over 500 cycles.