Abstract
The properties of hybrid Sn-based artificial SEI layers in protecting Li metal electrode towards surface instabilities were investigated via a combined experimental and theoretical approach. The performance of coating layers can be coherently explained based on the nature of the coating species. Notably, when starting from a chloride precursors, the hybrid coating layer is formed by an intimate mixture of Li 7 Sn 2 and LiCl: the first ensures a high bulk ionic conductivity, while the second forms an external layer allowing a fast surface diffusion of Li + to avoid dendrite growth, a low surface tension to guarantee the thermodynamic stability of the protective layer and a negative underneath plating energy (UPE) promoting lithium plating at the interface between Li metal and the coating layer. The synergy between the two components, and in particular the crucial role of LiCl in the promotion of such an underneath plating mechanism, are shown to be key properties to improve the performance of artificial SEI layers.