Size‐Induced High Entropy Effect for Optimized Electrolyte Design of Lithium‐Ion Batteries

Electrolyte design is critical for high energy lithium-ion batteries (LIBs) but is struggling with the trade-offs between conductivity and stability. Increasing electrolyte entropy can improve the conductivity without compromising stability. A size-induced high entropy effect is identified for electrolyte design, which increases configurational entropy and is more pronounced than conventional number-induced high entropy effect. The developed size-induced high-entropy electrolyte (HEE) with small-sized esters exhibits enhanced configurational diversity and entropy, resulting in smaller Li+ solvation clusters, a lower freezing point (-96.6 °C), threefold higher ionic conductivity at -60 °C, improved wettability and facilitated Li+ de-solvation compared to conventional number-induced HEE. These advantages contribute to more uniform Li deposition and the formation of a robust and thin cathode-electrolyte interphase (CEI) on LiNi0.8Co0.1Mn0.1O2 (NCM811). Consequently, Li || NCM811 employing the small-sized HEE (SHEE) demonstrates superior cycling stability for 2000 cycles at a decay rate of 0.0162%/cycle under 10 C, and an exceptional rate capability under ultralow temperatures, i.e., capacity retention of 84.3% at -60 °C. A 1.0 Ah graphite || NCM811 pouch cell further exhibits 97.7% capacity retention for 300 cycles. The size-induced high entropy design strategy of electrolyte promises practical operation of LIBs under extreme conditions.