Bifunctional fluoropyridinium-based cationic electrolyte additive for dendrite-free Li metal anode

Although lithium metal has become a promising anode material for high-energy batteries owing to its high specific capacity and the lowest reduction potential, the continuous side reactions with electrolyte as well as the safety problem caused by Li dendrite growth restrict Li anode’s practical application. Herein, we demonstrate that N-fluoropyridinium (ArF⁺) bis(trifluoromethane)sulfonimide (TFSI⁻) as an electrolyte additive can protect the lithium metal by both solid electrolyte interphase (SEI) protection and electrostatic repulsion mechanisms. The ArF⁺ cations not only participate in forming F, N-containing SEI protective layer on Li surface, but also act as a cationic repellent during Li deposition to inhibit Li dendrite growth. As a result, the cycle performance of Li symmetric cells and Li||LiFePO₄ full cells were significantly improved by using ArFTFSI-added electrolyte. This study provides an electrolyte additive strategy for Li anode realizing SEI protection and electrostatic repulsion simultaneously.