Fire safety challenge of lithium metal batteries and advanced strategies for improving intrinsic safety

Abstract

The high energy density of lithium metal batteries (LMBs) has attracted widespread attention, which is expected to improve the endurance mileage of electric vehicles comparable to fossil fuel-powered vehicles. At present, the main research is focused on developing advanced materials and revealing the in-depth electrochemical mechanism of LMBs, while there is a significant lagging behind of attention to the safety evaluation. This review aims to emphasize the fire safety challenges faced by LMBs and summarize advanced strategies for improving intrinsic safety. Firstly, the basic chemical composition and working principle of LMBs were introduced compared with lithium-ion batteries. Moreover, we reviewed the thermal runaway problem of LMBs from the aspects of material activity, interfacial stability triggering conditions, thermal runaway behavior and mechanism, the special thermal runaway characteristics, and new safety challenges of Li-S, Li-O₂, and the solid-state LMBs were discussed in detail. Based on the analysis of the thermal runaway mechanism, we summarized the advanced strategies, including electrolyte design, interphase film construction, separator, and anode design for improving the intrinsic safety of LMBs. Finally, we proposed the fire safety challenge at the battery level and emphasized the necessity of designing safe materials based on the thermal runaway mechanism. Blocking the thermal coupling reaction and conducting multi-strategy collaborative optimization is the key point to restrain thermal runaway.