Towards establishing uniform metrics for evaluating the safety of lithium metal batteries

Lithium metal batteries (LMBs) with ultra-high theoretical energy densities are regarded as excellent candidates for the next energy storage devices. Unfortunately, there are many factors can cause the temperature of LMBs to exceed a safe range and trigger thermal runaway. Countless effort has been invested in designing safe components of batteries to realize the application of LMBs. However, most studies only focus on one single aspect since there is no uniform metrics for evaluating the safety of LMBs. Herein, this review comprehensively summarizes all the trigger factors of thermal runaway and proposes the complete safety metrics of LMBs. A comprehensive overview of the development of safe LMBs is provided to discuss the gap between studies and practical applications. Finally, the future directions of academic research are proposed according to the challenges existing in current studies.