Hydrometallurgical recycling of lithium-titanate anode batteries: Leaching kinetics and mechanisms, and life cycle impact assessment

Abstract

Since the inception of Li-ion batteries, the chemistry of cathode and anode materials has changed time-to-time. In recent times, the lithium-titanate (LTO) anode material has gained attention due to a higher surface area (100 m2/g) than the usual graphite-made anode (3 m2/g). The development of a new recycling strategy, in particular, to deal with spent LTO batteries, is therefore urgently needed as plenty of batteries deployed in electric vehicles are near to completing their lifespan. Herein, we demonstrate the recycling of spent LTO batteries by optimizing the parametric influence of H2SO4 concentration, H2O2 dosage, agitation speed, temperature, and time for lithium and titanium leaching from the anode material. About 92% titanium and 98% lithium were efficiently leached from the anode powder using a 3.5 mol/L H2SO4 solution with 25 vol% H2O2 at a pulp density of 5 wt./vol.%, temperature 120 °C, and time 120 min. The leaching examined in the temperature range between 60 °C and 120 °C with respect to time showed the best fits to the kinetic model governed by the logarithmic rate law. The apparent activation energies of titanium (78.9 kJ/mole) and lithium (11.3 kJ/mole) indicated two different mechanisms governed by chemically controlled and diffusion-controlled reactions, respectively. It indicated that both metals’ leaching proceeded through lixiviant diffusion on the LTO surface, which was corroborated by the instrumental analyses of the untreated LTO sample and the leached residues. A life-cycle assessment suggests the need for discharge acid for recycling within the system due to a terrestrial ecotoxicity of 97.09 kg DCB-eq; however, the ionizing radiation and eutrophication potential are found to be negligible.