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 °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.