Direct insights into the electrochemical processes at anode/electrolyte interfaces in magnesium-sulfur batteries

Magnesium-sulfur (Mg-S) batteries are highly attractive because of their high theoretical energy density, low cost and safety features. However, severe capacity fading issues limit their development, which are greatly associated with reaction processes at electrode/electrolyte interfaces. Herein, we systematically studied the interfacial processes of Mg deposition/stripping in ether-based electrolytes at nanoscale by in situ atomic force microscopy (AFM). It can be directly observed the initial nucleation of bowl-like structure and deposition of crystallized Mg upon charge in tetraglyme (TEG) - based electrolyte, followed with uniform stripping process upon discharge. In contrast, the initial nucleation of bowl-like structure, fast stack of nanoparticles (NPs) and deposition of crystallized Mg upon charge can be observed in diglyme (DEG) - based electrolyte, followed with nonuniform stripping process upon discharge. Combined with in situ optical imaging, former system shows better reversibility upon cycle. The present results reveal a direct insight into the structure-reactivity correlation at anode/electrolyte interfaces, which provides deep understanding of the interfacial mechanism to guide the design and development of the high-energy Mg-S batteries.