Enhanced performance in lithium metal batteries: A dual-layer solid electrolyte interphase strategy via perfluoropolyether derivative additive

The utilization of metallic lithium at the negative electrode is regarded as the most promising approach to enhance the energy density of current lithium battery systems. However, uncontrolled lithium dendrite growth leading to instability and low coulombic efficiency (CE) hinders the practical application of metallic lithium as the negative electrode. This study unveils the synthesis of a perfluoropolyether (PFPE) derivative electrolyte additive, denoted as PPP, through reversible addition-fragmentation chain transfer (RAFT) polymerization involving 2-butylsulfanyl-thiocarbonylsulfanyl-propionic acid (PABTC), PFPE and polydioxolane acrylate (PDXLA) as precursors. This additive incorporates fluorinated segments to enhance lithium ion transport efficiency, along with organic segments to improve battery stability. It facilitates the formation of a distinctive dual-layered solid electrolyte interphase (SEI) in 1,3-dioxolane (DOL) based lithium metal batteries. The upper organic protective layer mitigates volume deformation and suppresses lithium dendrite growth, while the lower dense LiF layer enhances lithium ion transport rates, thus improving battery performance. The resulting dual-layer SEI structured LFP | DOL-PPP | Li cell exhibits a capacity retention of 94.1 % after 150 cycles. Moreover, the Li | DOL-PPP | Li cell demonstrates stable cycling performance exceeding 1800 h at 0.2 mA cm^-2. This work underscores the significant potential of PFPE derivatives as electrolyte additives in the design and optimization of lithium batteries.