Sustainable Recycling of Spent Asymmetric-Capacitance Power Batteries

There is a pressing need to recover asymmetric-capacitance nickel-metal hydride power batteries (AC-NiMHs) owing to their large number of applications. However, recycling of these batteries is challenging since it is a long process with low extraction efficiency and high cost. Herein, we demonstrate a sustainable, green, and effective recovery process for rare earth metals while directly preparing LiNi_0.6Co_0.2Mn_0.2O₂ cathodes from cathode and anode AC-NiMH spent materials. We investigate the effects of a range of parameters (i.e., acid concentration, reaction temperature, and time) on the leaching process. Over 99% of rare earth, Co, Ni, and Mn are leached out during the recovery process, with the leaching kinetics following a shrinking core model with inter-diffusion as the rate-determining step. Rare earths are recovered in the form of high-purity sulfuric acid complex salts, while Ni, Co, and Mn are used to synthetize LiNi_0.6Co_0.2Mn_0.2O₂ cathodes with good electrochemical properties. This research demonstrates a sustainable process for the recycling of power sources by incorporating the principles of green chemistry.