Tuning Solid Electrolyte Interphase Layer Properties through the Integration of Conversion Reaction.

The solid electrolyte interphase (SEI) layer plays an important role in altering the ion transport and modifying the structural evolution of the Li metal anode during repeated cycling. While the fundamental understanding of the SEI properties has been continuously advanced in recent years, effectively tuning the SEI components, especially the inorganic constituents, is still challenging. In this work, tungsten trioxide, WO3, is found to promote the formation of inorganic salts, for example, LiF/Li2CO3 in SEI layers, thereby enhancing the SEI properties such as mechanical and chemical stabilities. Additionally, WO3 is simultaneously reduced to electronic W nanoparticles during the electrochemical process, mitigating the formation of "dead" Li, which otherwise is completely wrapped by the accumulated insulating SEI layers. The possibility of WO3 in catalyzing electrolyte decomposition, through favored reaction pathway, to produce robust SEI layers is discussed. This work provides new insights into the control of the SEI properties on Li metal surfaces.