Facile Oxidative Recovery of Manganese as Electrochemically Active MnO₂ from Spent Lithium-Ion Battery Bioleachate

In view of the rapidly growing volumes of spent lithium-ion battery (LIB) waste being generated annually, there is an urgent need to develop novel and green approaches to recover critical metals from spent LIBs in the form of technologically valuable materials for reincorporation back into battery manufacturing to achieve a circular economy for electronic waste. This study reports facile persulfate-mediated selective recovery of manganese as electrochemically active manganese dioxide (MnO₂) from nickel manganese cobalt (NMC)-based spent LIB black mass (60 mesh) after processing via an environmentally friendly bioleaching technique. X-ray diffraction (XRD), scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDX), and inductively coupled plasma-optical emission spectroscopy (ICP-OES) characterizations of recovered precipitate from optimized persulfate treatment of bioleachate solution using 0.3 M sodium persulfate (Na₂S₂O₈) have confirmed it to be MnO₂ of 90% purity comprising δ-MnO₂ and γ-MnO₂ phases, possessing distinct spherical nanoflower morphology. Electrochemical evaluation studies of the bioleachate recovered MnO₂ for aqueous zinc battery application revealed that bioleachate MnO₂ demonstrated a comparable discharge capacity of 145 mAh/g in alkaline electrolyte as well as much superior cycling performance (81% retention of initial discharge capacity of 149 mAh/g) for up to 80 cycles in a mildly acidic ZnSO₄-based electrolyte than commercial MnO₂. The oxidative recovery of Mn as MnO₂ using sodium persulfate from spent LIB bioleachates is promising for the selective removal of Mn from battery leachates and upcycling of Mn from end-of-life LIBs into high-purity MnO₂ to serve as cathodes for aqueous zinc battery applications.