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

Abstract

The operation of lithium-ion batteries (LIBs) at low temperatures (≤−20 °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)||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 °C. It also sustains stable charge and discharge cycling at −40 °C with 60% capacity retention compared with room-temperature operation. This outstanding electrochemical performance is further supported by electrochemical impedance spectroscopy (EIS) in three-electrode 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.