Ionic Liquid-Based Electrolytes for High-Voltage Li-Ion Batteries

Abstract

The lithium-ion battery (LIB) with high energy density is highly demanded for electric vehicle application. To increase the energy density of LIB, one popular approach is to elevate the operation potential of the cathode or the voltage of the cell. However, at high potentials or high voltages, the state-of-the-art (SOA) organic carbonate-based electrolytes tend to be oxidatively decomposed at the cathode surface causing gassing issue, low Coulombic efficiency, transition metal ion dissolution and rapid capacity fade of the full cell. In this presentation, we studied the piperidinium-based ionic liquids as an electrolyte candidate for high-voltage lithium-ion battery due to their low melting point, low vapor wide electrochemical window, nonflammability and low/non-volatile merits. When doped with various amount of lithium fluorosulfonylimide salt (LiFSI), the piperidinium-FSI- based ionic liquid showed much improved cycling performance in the NMC532/Li cells at voltages higher than 4.5 V compared with the SOA electrolyte - 1.2 M LiPF6 EC/EMC (3/7 wt.). The feasibility as a practical electrolyte for the next generation LIB was evaluated by its physical properties and electrochemical stability on both cathode and anode. Furthermore, Raman spectroscopy and molecular dynamic simulations (MD) were conducted shedding light on the sophisticated 3D-network structure containing piperidinium cation, FSI- and Li+ species at various LiFSI concentrations.