Novel piperidinium-based ionic liquid as electrolyte additive for high voltage lithium-ion batteries

Conventional carbonate-based electrolyte is prone to oxidative decomposition at high voltage (over 4.5 V vs. Li/Li+), which leads to the bad oxidation stability and inferior cycling performance of lithium ion batteries (LIBs). To solve these problems, a novel ionic liquid (IL) N-butyronitrile-N-methylpiperidinium bis(fluorosulfonyl)imide (PP1,CNFSI) was synthesized and explored as the additive to the LiPF6–ethylene carbonate (EC)/dimethyl carbonate (DMC) electrolyte. For the cell performance, the addition of PP1,CNFSI not only inhibits overcharge phenomenon, but also improves discharge capacity, thus enhancing capacity retention capability. Compared to the cell with blank electrolyte, the capacity retentions of adding 15 wt% PP1,CNFSI into the electrolyte were improved to 96.8% and 97% from 82.8% and 78.7% at 0.2 C and 5 C, respectively. The effects of PP1,CNFSI on the LNMO cathode surface were further investigated by electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). It reveals that PP1,CNFSI addition drives the formation of solid electrolyte interphase (SEI) film which suppresses oxidative decomposition of the electrolyte and protects the structure cathode material.