Functional electrolyte additives can improve the stability and safety of high voltage lithium-ion batteries. A mixture of fluoroethylene carbonate (FEC) and succinonitrile (SN) in a carbonate-based electrolyte improved the cycling stability and electrochemical stability window of a LMNO−Li device. The FEC+SN electrolyte also exhibited better thermal stability using operando accelerating rate calorimetry (ARC) by virtue of its reduced heat generation.