Stability of solid electrolyte interphases and calendar life of lithium metal batteries

Lithium (Li) metal batteries (LMBs) are a promising candidate for next generation energy storage systems. Although significant progress has been made in extending their cycle life, their calendar life still remains a challenge. Here we demonstrate that the calendar life of LMBs strongly depends on the surface area of Li metal anodes exposed to the electrolyte and can be significantly improved by forming a stable solid electrolyte interphase (SEI) layer on the LMA surface. The stability and role of the accumulated SEI stacks are studied in their entirety in this work, beyond the conventional SEI investigations that focus on the local microscopic structure of a single SEI. Furthermore, we reveal, for the first time, the stability and reusability of this SEI during repeated lithium stripping/deposition processes using room temperature in situ electron microscopy. It is also demonstrated in this work that lithium anodes exhibit a much smaller active surface area under either fully charged or fully discharged conditions. Therefore, LMBs stored under these conditions exhibit a much longer calendar life than those stored at an intermediate state of charge. These findings reveal the most critical factors affecting the calendar life of LMBs and several approaches for improving both design and operation of these batteries to extend their calendar life have been proposed. Robust, flexible, and reusable solid electrolyte interphases and a minimal lithium/electrolyte interface area endow lithium metal batteries with a long-term calendar life.