Enabling the Low-Temperature Cycling of NMC∥Graphite Pouch Cells with an Ester-Based Electrolyte

The operation of lithium-ion batteries (LIBs) at low temperatures (<=-20 degrees C) is limited by reduced ionic transport properties of the electrolyte, as well as by severe charge-transfer polarization. Herein, we demonstrate that this low-temperature cycling limitation can be overcome in LiNixMnyCozO2 (x + y + z = 1) (NMC)|parallel to graphite type full cells with a methyl propionate (MP)-based ester electrolyte. This electrolyte, consisting of LiPF6 dissolved in MP and fluoroethylene carbonate (FEC), delivers successful cycling at the high rate of 0.5C at -20 degrees C. It also sustains stable charge and discharge cycling at -40 degrees C with 60% capacity retention compared with room-temperature operation. This outstanding electrochemical performance is further supported by electrochemical impedance spectroscopy (EIS) in threeelectrode pouch cells to investigate the internal resistances between cathode and anode, as well as careful structure and composition characterizations at the electrode interfaces. This work offers a new avenue for high-performance LIBs capable of ultralow-temperature charging-discharging operation.