Flame-retardant oligomeric electrolyte additive for self-extinguishing and highly-stable lithium-ion batteries: Beyond small molecules

Preparing both safe and high-performance lithium-ion batteries (LIBs) based on commonly used commercial electrolytes is highly desirable, yet challenging. To overcome the poor compatibility of conventional small-molecular flame-retardants as electrolyte additives for safe LIBs with graphite anodes, in this study, we propose and design a novel low-cost flame-retardant oligomer that achieves an accurate and complete reconciliation of fire safety and electrochemical performance in LIBs. Owing to the integration of phosphonate units and polyethylene glycol (PEG) chains, this oligomer, which is a phosphonate-containing PEG-based oligomer (PPO), not only endows commercial electrolytes with excellent flame retardancy but also helps stabilize the electrodes and Li-ion migration. Specifically, adding 15 wt% of PPO can reduce 70% of the self-extinguishing time and 54% of total heat release for commercial electrolytes. Moreover, LiFePO4/lithium and graphite/lithium cells as well as LiFePO4/graphite pouch full cells exhibit good long-term cycling stability.