Analysis of Degradation and Electrochemical Behavior of Lithium–Oxygen Batteries under Lean Electrolyte Conditions

Lithium–oxygen batteries have garnered much attention in the past decades due to their high energy density and active material abundancy. Decreasing the electrolyte volume is critical to achieving a high energy density for practical applications. Recent works have demonstrated a serious performance limitation at lower electrolyte fillings. In this work, we study specifically the difference between flooded and lean electrolyte lithium–oxygen batteries by systematically tracing the source of performance degradation. We find that the key contributor to the decrease in performance under lean electrolyte conditions stems from the lithium metal anode rather than the cathode. Solid electrolyte interphase (SEI) compositionally appears to be the same from X-ray photoelectron spectroscopy but the coverage is less uniform, and impedance is much higher under lean electrolyte conditions. Such an effect likely produced the observed poorer cycle performance at 10 μL cm–2 (∼28% cathode’s pore volume filled) vs 100 μL cm–2 (278% of cathode’s pore volume) at a capacity of 1.0 mAh cm–2 (0.1 mAh cm–2) using an electrolyte composition of 1 M LiTFSI in TEGDME.