Regulating the solvation structure of an acetonitrile-based electrolyte for Li/NMC811 batteries cycled at low temperature

Abstract

LiNi_xMn_yCo_1−x−yO₂ (NMC) cathode materials with Ni ≥0.8 have garnered significant interest for their potential in high energy-density lithium metal batteries (LMBs). However, their performance at low temperatures (−20 °C and below) is hindered by increased resistance encountered by Li⁺ transport within the bulk electrolyte and across the electrolyte/electrode interfaces, resulting in capacity loss and battery failures. Acetonitrile (AN) is a well-known organic solvent with low viscosity, low melting point and high dielectric constant. However, the incompatibility issue of AN with anode and cathode materials hindered its application. Herein, we have developed a localized high-concentration AN-based electrolyte (LHCE) comprising lithium bis(fluorosulfonyl) imide (LiFSI) salt, AN solvent and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) diluent. The LHCE promotes the formation of an anion-derived cathode–electrolyte interface (CEI) on the NMC811 surface, thereby reducing the charge transfer resistance and facilitating Li⁺ transport at sub-zero temperatures. The exemplary electrolyte enables NMC811-based LMBs to achieve excellent cycling stability at −30 °C and superior low-temperature charge–discharge performance down to −40 °C with a discharge specific capacity of 113 mA h g⁻¹ at 0.1C rate.