Competitive nucleation and growth behavior in Li-Se batteries

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.