Abstract
Li-ion batteries intended to operate over extremes in temperature or at cell voltages approaching 5 V exceed the fundamental capabilities of the electrolytes presently available. The most promising solvents that do meet the fundamental requirements exhibit exceptional instability at the low potentials found with negative electrodes of Li-ion batteries today. Herein, nitrile and linear carbonate electrolytes were stabilized with only the use of a small percentage of additives to enable formulations that may be of use for low temperature and high voltage operating conditions, respectively. In this work, the electrochemical characteristics of Li-ion cells were explored for a variety of electrolytes, with promising performance identified in systems composed predominantly of ethyl methyl carbonate (EMC), 3-methoxypropionitrile (3MPN), or adiponitrile (ADN). Vinylene carbonate (VC) and monofluoroethylene carbonate (FEC) were added in low concentrations (≤5 vol%) to stabilize the interface of the carbon negative electrode and the electrolyte, with FEC proving to be effective across all electrolytes examined herein. The fluoride decomposition products of FEC contributing to the SEI have been identified for the first time without the presence of lithium hexafluorophosphate (LiPF6) in the electrolyte, thereby leading to a clearer explanation of its exceptional protective effect within the SEI.