Insight into the Contribution of Nitriles as Electrolyte Additives to the Improved Performances of the LiCoO2 Cathode

Nitriles have been successfully used as electrolyte additives for performance improvement of commercialized lithium-ion batteries based on the LiCoO(2 )cathode, but the underlying mechanism is unclear. In this work, we present an insight into the contribution of nitriles via experimental and theoretical investigations, taking for example succinonitrile. It is found that succinonitrile can be oxidized together with PF6- preferentially on LiCoO2 compared to the solvents in the electrolyte, making it possible to avoid the formation of hydrogen fluoride from the electrolyte oxidation decomposition, which is detrimental to the LiCoO2 cathode. Additionally, inorganic LiF and -NH group-containing polymers are formed from the preferential oxidation of succinonitrile, constructing a protective interphase on LiCoO2, which suppresses electrolyte oxidation decomposition and prevents LiCoO2 from structural deterioration. Consequently, the LiCoO(2 )cathode presents excellent stability under cycling and storing at high voltages.

Automated summary

This study investigates the mechanism of nitrile additives in improving the performance of commercialized lithium-ion batteries. The results show that nitrile compounds can preferentially oxidize on LiCoO2, forming a protective interphase and suppressing electrolyte oxidation decomposition, thereby enhancing the stability of the LiCoO2 cathode.