Importance of Halide Ions in the Stabilization of Hybrid Sn-Based Coatings for Lithium Electrodes

The properties of hybrid Sn-based artificial solid electrolyte interphase (SEI) layers in protecting Li-metal electrodes toward 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 precursor, the hybrid coating layer is formed by an intimate mixture of Li7Sn2 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) to promote lithium plating at the interface between the 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 the key properties to improve the performance of artificial SEI layers.

Automated summary

The properties of hybrid Sn-based artificial solid electrolyte interphase (SEI) layers in protecting Li-metal electrodes were investigated. The performance of the coating layers is dependent on the nature of the coating species. A hybrid coating layer formed from a chloride precursor, Li7Sn2 and LiCl, exhibits high bulk ionic conductivity, fast surface diffusion of Li+, low surface tension, and a negative underneath plating energy (UPE), which promote lithium plating and ensure the stability of the protective layer. The interaction between LiCl and Li7Sn2 is crucial for the improved performance of artificial SEI layers.