Design principles for self-forming interfaces enabling stable lithium-metal anodes

The path toward Li-ion batteries with higher energy densities will likely involve use of thin lithium (Li)-metal anode (<50 mu m thickness), whose cyclability today remains limited by dendrite formation and low coulombic efficiency (CE). Previous studies have shown that the solid-electrolyte interface (SEI) of the Li metal plays a crucial role in Li-electrodeposition and -stripping behavior. However, design rules for optimal SEIs are not well established. Here, using integrated experimental and modeling studies on a series of structurally similar SEI-modifying model compounds, we reveal the relationship between SEI compositions, Li deposition morphology, and CE and identify two key descriptors for the fraction of ionic compounds and compactness, leading to high-performance SEIs. We further demonstrate one of the longest cycle lives to date (350 cycles for 80% capacity retention) for a high specific-energy Li parallel to LiCoO2 full cell (projected >350 watt hours [Wh]/kg) at practical current densities. Our results provide guidance for rational design of the SEI to further improve Li-metal anodes.