Lithium-metal batteries (LMBs) are promising alternatives to state-of-the-art Lithium-ion batteries (LIBs) to achieve higher energy densities. However, the poor cyclability of LMBs resulting from Li metal anode (Li⁰) irreversibility and concomitant electrolyte decompositions limits their practical applications. In the last decades, advanced Li-ion electrolytes, additives, and electrolyte solvents have been extensively exploited to improve the cycling stability of Li⁰. In this study, we reported a novel and economical approach to suppress dangerous Li dendrite morphologies using a synthesized per-fluorinated salt additive, lithium tetrakis(perfluoro-tertbutyloxy)borate (abbreviated as Li-TFOB), which contains 36 F atoms per molecule. This newly designed ionic additive tuned the chemical composition of the solid-electrolyte interphase (SEI) on Li⁰ by increasing the amount of LiF and Li-B-O inorganic species. DFT calculations indicated the preferential reduction of the TFOB anions at Li⁰, which occurs with a lower free energy change PF₆^- anions. Molecular dynamics (MD) simulations using polarizable force fields were conducted to reveal the interfacial structures on Li⁰ at the instant before SEI formation. The bulky TFOB anions apparently took a prominent presence at a distance closer to the Li⁰ surface, making TFOB more likely to be reduced than PF₆^- and hence rendering its reduction products the major components in SEI. This experiment-simulation joint study illustrated an attractive approach to accelerating the design of electrolytes and interphases for LMBs.

Tianbiao Liu

Utah State University

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