Formation and Growth Mechanisms of Solid-Electrolyte Interphase Layers in Rechargeable Batteries

Battery technology is advancing rapidly with new materials and new chemistries; however, materials stability determining battery lifetime and safety issues constitutes the main bottleneck. Electrolyte degradation processes triggered by electron transfer reactions taking place at electrode surfaces of rechargeable batteries result in multicomponent solid-electrolyte interphase (SEI) layers, recognized as the most crucial yet less well-understood phenomena impacting battery technology. Electrons flow via tunneling from the bare surface of negative electrodes during initial battery charge causing electrolyte reduction reactions that lead to SEI nucleation, but the mechanisms for further growth beyond tunneling-allowed distances are not known. Our first-principles computational studies demonstrate that radical species are responsible for the electron transfer that allows SEI layer growth once its thickness has evolved beyond the electron tunneling regime. In addition, the composition, structure, and properties of the SEI layer depend on the electrolyte, especially on the extent to which they are able to polymerize after reduction. Here we present a detailed study of polymerization mechanisms and propose mechanistic differences for electrolytes yielding a fast and a slow SEI growth. This new understanding leads to firm guidelines for rational electrolyte design.