Pathway of in situ polymerization of 1,3-dioxolane in LiPF6 electrolyte on Li metal anode

Abstract

Although the lithium metal battery has been considered to be one of the most promising candidates to facilitate high-density energy storage, the practical applications of lithium metal anodes are significantly hindered by its high reactivity. Electrolytes based on 1,3-dioxolane (DOL) have been demonstrated to be one of the most effective electrolytes that can suppress side reactions, but the underlying mechanism is still far from clear. In this work, we carried out multi-scale simulations that combine density functional theory (DFT) and reactive force field (ReaxFF) to investigate the initial reactions of 1.0 M LiPF6 salt in DOL with Li metal anode. Our simulation results reveal that PF6− anions can either fully decompose via reduction reaction when they directly in contact with Li anode or convert to PF5 when they stay in bulk. While the decomposition products (F− and Px−) contribute to the formation of the inorganic part of the solid electrolyte interphase (SEI), the latter PF5 can serve as an initiator of the polymerization of DOL. Such polymerization of the electrolyte provides an unexpected protective effect that resembles the polymer electrolyte but is formed in situ. The most kinetically favorable polymerization pathway is then distinguished from hybrid functional DFT calculations, which confirms that PF5 plays an important role in activating the DOL ring for further polymerization. The insights revealed from this work should be of help to expedite the rational design of electrolytes that provide protective SEI to stabilize Li anode.