Design of functional electrolytes using triple-bonded formate esters as SEI forming additives in graphite anodes

The concept of functional electrolytes, in which small amounts of additives are added to the electrolyte to improve the performance of lithium-ion batteries (LIBs), is widely used around the world. Our laboratory has been researching the use of carbonates and sulfonate esters containing triple bonds as additives for solid electrolyte interphase (SEI) formation in anodes and for suppressing the corrosion of Al current collectors. In contrast, formate esters are generally thought to be susceptible to oxidative and reductive decomposition and corrosion. In this work, we attempted to introduce a triple bond into the formate ester, which has currently not received much attention. As a result, we found that the formate ester with a cyanomethyl (-CH 2 C≡N) group exhibits excellent cycling performance when added in very small amounts. • Cyanomethyl formate (CMF) is a new SEI-forming additive for graphite anodes. • CMF has a higher reductive and oxidative decomposition potentials than VC. • CMF has low molecular weight, thin SEI, and low cell impedance. • CMF does not easily cause Al corrosion.