Safe and efficient phosphonium ionic liquid based electrolyte for high-potential LiMn2O4 and LiNi0.8Co0.15Al0.05O2 cathodes for Li-ion batteries

Abstract

Electrolytes are essential constituents for safe and reliable battery performance. Current lithium-ion battery (LIB) systems present an inherent safety problem stemming from the use of metal oxide cathodes, which are oxygen sources, and flammable electrolytes based primarily on organic carbonates. Herein we report a novel non-flammable electrolyte formulated by the addition of 30% wt. of methyltributhylphosphonium Bis(trifluoromethanesulfonyl) imide [Bu3MeP][TFSI] ionic liquid (IL) to a standard electrolyte (SE, ethylene carbonate (EC): ethyl methyl carbonate (EMC) 1:1 wt/wt) + 1M LiPF6). The good physicochemical properties of the IL, (i) mitigate the ignition delay and flammability of the proposed electrolyte and (ii) markedly improve the interfacial resistance of the LiMn2O4//Li and LiNi0.8Co0.15Al0.05O2//Li half-cells. The half-cells' performance indicates that the conveyed hybrid electrolyte (HE) retains a higher portion of its energy density (629 vs. 446 Wh.kg−1 for HE and SE in an NCA//Li half-cell, accordingly). At 60°C, [Bu3MeP] [TFSI] considerably improved the cathode performance in terms of capacity (up to 230 mAh.g−1 for NCA) and coulombic efficiency (>99%).