Activation of Glass-State Selenium Driven by Deep-Discharge Cycling for High-Loading Se/Carbon Cathode

Improving the Se utilization of the high-loading Se/carbon cathode is of great importance in the development of lithium–selenium (Li–Se) batteries. As revealed in our previous report, the low Se utilization rate under a high load is closely related to the glass-state structure of confined Se at room temperature. In this study, we present an in situ electrochemical activation strategy based on deep-discharge mode for activating glass-state structures to achieve high Se utilization in mesoporous carbon. It is found that deep discharge with a cutoff voltage of 0.5 V significantly promotes the glass Se to Li 2 Se conversion, and the delithiation of Li 2 Se regenerates amorphous Se of shorter chains during the subsequent charging process for 70 and 80 wt % Se@CMK-3 cathodes. The regenerated amorphous Se has lower glass transition temperature and is in the rubbery state at room temperature. This electrochemical cycle-driven transition, from a long-chain glass state to a short-chain rubbery state, largely promotes Li + diffusion and Se reactivity, thus enhancing the Se utilization rate. In particular, the Se utilization rate for 70% Se@CMK-3 is increased to 89.4% under deep-discharge cycling (3.0–0.5 V) from 41.4% under a normal voltage window (3.0–1.0 V). The deep-discharge method provides a practical approach to overcome the transport limitations of glassy Se for developing high-energy-density Li–Se cathodes.