Understanding and Suppressing Gas Evolution in Lithium Metal Batteries with Ether-Based Electrolytes

Understanding and suppressing gas evolution in lithium secondary batteries are critical to optimizing battery performance and ensuring safe operation.^1,2 However, no systematic investigations of gas evolution in ether-based lithium metal batteries (LMBs) have been conducted despite the enticing prospects of LMBs for achieving ultrahigh energy density.^3–5 In this work, gas generation in ether electrolyte-based LMBs was quantified and the underlying redox mechanisms were elucidated. Through studying cathode and anode half-cells, it was determined that CO₂ and CO gas were generated at the cathode and CH₄ gas at the anode. Notably, CO₂ and CO were not observed in the full cell as they were consumed at the anode, reacting with lithium to produce solid Li compounds such as Li₂CO₃. CH₄ generated at the anode is the major contributor of gas generated in the full cell, though its evolution during cycling is not immediate and occurs after an onset point. The total gas volume generated increases dramatically with increasing temperature and decreasing electrolyte concentration. Based on these findings, electrolyte engineering and anode surface activation strategies were explored to control CH₄ production and hence overall gas evolution. In particular, the anode activation approach resulted in increased Li nucleation sites and improved Li deposition morphology, leading to significantly suppressed interfacial reactions, thus delaying the onset of gas evolution by 800% and increasing the cycling life by 400%. Achieving these improvements without altering the electrolyte formulation demonstrates the potential broad applicability of anode activation across various electrolyte chemistries. The performance enhancements beyond merely suppressing gas generation advances the prospects of safer and higher-performing LMBs.