Towards high-voltage Li-ion batteries: Reversible cycling of graphite anodes and Li-ion batteries in adiponitrile-based electrolytes

Due to their low vapor pressure and their promising electrochemical and thermal stability, NC- (CH2)n-CN dinitriles are proposed as an electrolyte solvent for Li-ion batteries. Adiponitrile (ADN) has substantial advantages, especially for applications requiring high potential cathodes, because it has high electrochemical/thermal stability (up to 6 V vs. Li/Li+,> 120 °C). However, to obtain very high voltage batteries, ADN electrolytes must also passivate the anode of the battery. In this work, reversible cycling of graphite in adiponitrile was successfully achieved by adding a few percent of fluoroethylene carbonate allowing the realization of Graphite/NMC Li-ion battery. The battery of specific capacity of 135 mAhh.g−1 showed a cycling stability for more than 40 cycles. The composition of the solid electrolyte interphase (SEI) was determined as a function of the FEC concentration as well as the state of charge of the graphite anode using hard X-ray photoelectron spectroscopy (HAXPES) and XPS. With FEC, the SEI layer is thinner and depends on the SOC of the anode, but does not depend on the FEC concentration. SEM characterizations clearly showed that the surface of the anode is completely covered by the SEI layer, regardless of the concentration of FEC. Indeed, 2% of FEC is sufficient to suppress the reduction of adiponitrile which is explained by a specific adsorption of FEC on the graphite anode.