Voltage behavior in lithium-ion batteries after electrochemical discharge and its implications on the safety of recycling processes

The demand of lithium-ion batteries (LIBs) is exponentially increasing, largely due to the ongoing transition towards electric transportation. To support the raw material supply for LIB manufacturing, there are significant ongoing efforts to recycle battery materials. Nevertheless, end-of-life LIBs entering recycling processes may still contain remnant energy, representing a potential hazard during handling and processing. Despite the urgency to improve LIB recycling, there is a lack of serious discussion in the literature regarding discharging strategies for LIBs. The electrochemical discharge using aqueous salt solutions route for example, has been widely mentioned without proper evidence of its usefulness. Among the discharge phenomena so far overlooked is the voltage recovery effect of batteries (a.k.a. voltage rebound/relaxation), where battery power appears to spontaneously surge, even after readings of full discharge in a circuit. In this work, a systematic study on the behaviour of LIBs during discharge in aqueous salt solutions is presented to better understand this unit process, addressing the challenges to fully drain energy from spent batteries prior to recycling. We demonstrate that the voltage recovery effect creates false readings for the battery charge level that represent risks during processing. If electrochemical discharge is employed, we present a methodology to decrease open circuit voltage in aqueous salt solution to 2.0 V, suitable for mechanical processing.