Competitive nucleation and growth behavior in Li–Se batteries

Abstract

As a promising cathode material, selenium has attracted a great deal of research interest due to its high theoretical capacity analogous to sulfur in lithium–chalcogen batteries. However, unlike S cathodes, mechanistic understanding including fundamental observations on the formation of Li₂Se and Se deposits, and their dissolution in Se cathodes remains at an early stage. Here, we directly visualize the dissolution and deposition reactions of Se cathodes using operando transmission X-ray microscopy, and build a nucleation site distribution map by tracking the individual solidification of electrolyte-soluble polyselenide intermediates into Se deposits. This real-time analysis reveals the nucleation behavior dependent on the depletion of polyselenides as well as the morphological characteristics through their subsequent growth, along with the different nucleation modes for particle-like Li₂Se upon discharge and dendritic Se upon charge. We further propose that appropriate operating conditions, prioritizing the nucleation over the growth, can effectively utilize Se, precluding the dendritic growth.