Ethylene‐Carbonate‐Free Electrolytes for Rechargeable Li‐Ion Pouch Cells at Sub‐Freezing Temperatures

• Published in: Advanced materials (Weinheim) Vol. 34; no. 45; pp. e2206448 - n/a
• Main Authors: Yao, Yu‐Xing, Yao, Nan, Zhou, Xi‐Rui, Li, Ze‐Heng, Yue, Xin‐Yang, Yan, Chong, Zhang, Qiang
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 01.11.2022
• Subjects: Charging; Electrolytes; Electrolytic cells; Ethylene; ethylene carbonate; Freezing; Ion transport; Li plating; Lithium-ion batteries; Li‐ion batteries; low‐temperature energy storage; Materials science; Melting points; organic electrolytes; Plating; Solid electrolytes; Temperature
• ISSN: 0935-9648; 1521-4095; 1521-4095
• DOI: 10.1002/adma.202206448

Sub‐freezing temperature presents a significant challenge to the survival of current Li‐ion batteries (LIBs) as it leads to low capacity retention and poor cell rechargeability. The electrolyte in commercial LIBs relies too heavily on ethylene carbonate (EC) to produce a stable solid electrolyte interphase (SEI) on graphite (Gr) anodes, but its high melting point (36.4 °C) severely restricts ion transport below 0 °C, causing energy loss and Li plating. Here, a class of EC‐free electrolytes that exhibits remarkable low‐temperature performance without compromising cell lifespan is reported. It is found that at sub‐zero temperatures, EC forms highly resistive SEI that seriously impedes electrode kinetics, whereas EC‐free electrolytes create a highly stable, low‐impedance SEI through anion decomposition, which boosts capacity retention and eliminates Li plating during charging. Pouch‐type LiCoO2 (LCO)|Gr cells with EC‐free electrolytes sustain 900 cycles at 25 °C with 1 C charge/discharge, and LiNi0.85Co0.10Al0.05O2 (NCA)|Gr cells last 300 cycles at −15 °C with 0.3 C charge, both among the best‐performing in the literature under comparable conditions. Even at −50 °C, the NCA|Gr cell with EC‐free electrolytes still delivers 76% of its room‐temperature capacity, outperforming EC‐based electrolytes. A new class of ethylene carbonate (EC)‐free electrolytes, based on methyl acetate and fluorinated ethers, is proposed for Li‐ion batteries operating at sub‐freezing temperatures. The EC‐free electrolyte demonstrates all‐round performance advantages over the traditional EC‐based electrolyte and presents a viable solution to improve the capacity retention and rechargeability of metal‐ion batteries in cold climates.