Simple, green organic acid-based hydrometallurgy for waste-to-energy storage devices: Recovery of NiMnCoC2O4 as an electrode material for pseudocapacitor from spent LiNiMnCoO2 batteries

Abstract

A simple, green approach to recover NiMnCoC2O4 as an electrode material for high-performance pseudocapacitors from spent LiNiMnCoO2 (NMC) batteries is proposed. Four strategic metals (Li, Ni, Co, and Mn) were leached from spent NMC batteries using several organic acids as model green leachants. Among the various candidates of green leaching agents, 2 M citric acid and 5 wt% glucose were selected as the leachant and reductant, respectively. Microwave irradiation was conducted during the leaching step to maximize the performance of the leaching rate and efficiency. The leaching efficiencies within 0.5 h for Ni(II), Li(I), Mn(II), and Co(II) were 90.7 ± 1.6%, 98.3 ± 2.4%, 94.9 ± 4.3%, and 95.6 ± 1.4%, respectively, and were thus as efficient as using aqua regia leaching. After the leaching process, divalent metal ions, that is, Ni(II), Co(II), and Mn(II), were immediately separated at room temperature using oxalic acid. The recovered samples were not further treated and used directly for energy storage applications. The recovered NiMnCoC2O4⋅nH2O has been demonstrated as a promising electrode for pseudocapacitors, providing a specific capacitance of 1641 F/g, good rate-retention capability (80% of low-current capacitance), and good cycle stability over 4000 charge–discharge cycles.