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

Abstract 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 LiNi 0.8 Co 0.1 Mn 0.1 O 2 (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.