Tertiary polymines as additives to lithium-ion battery electrolytes

摘要

Pentamethyldiethylenetriamine (PMDT), tetra(ethylene glycol) dimethyl ether (tetraglyme), and the crown ether 12-Crown-4 were investigated as electrolyte additives for lithium-ion cells using graphite anodes. Cyclic voltammetry at glassy carbon electrodes in 1M LiPF_6/propylene carbonate (PC) solutions containing pMDT, 12-Crown-4 or tetraglyme additive showed that the PMDT additive was electrochemically oxidized at approx 3.5 V vs. lithium reference. The 12-Crown-4 and tetraglyme, on the other hand, were found to be stable to approx 4.5 V where the control electrolyte without any additive was oxidized. Ionic conductivity measurements of the same solutions showed that all three additives enhanced the conductivity of 1 M LiPF_6/PC solution at 25 deg C. Lithium cycling studies in PC solutions using graphite electrodes showed that the 12-Crown-4 and tetraglyme additives allowed reversible lithium intercalation into graphite, whereas PMDT additive did not have any effect. However, PMDT additive was found to reduce the irreversible capacity loss on the first cycle in ethylene carbonate-propylene carbonate electrolyte solutions.