Amide compounds as electrolyte additives for improving the performance of high-voltage lithium-ion batteries

The influences that two amide-containing electrolyte additives, N,N-dimethyltrifluoroacetamide (DMTFA) and N,N-dimethylacrylamide (DMAA), have on the cycling stability of LiNi0.5Co0.2Mn0.3O2 (NCM523)/graphite cells were evaluated over a voltage range of 3-4.6 V. The results indicate that the capacity retention and Coulombic efficiency of the cells after cycling were improved by the addition of 3 vol.% DMTFA or DMAA to LiPF6-based electrolytes. The possible mechanisms behind the improvements were investigated using both theoretical calculations and experimental characterization. The results show that both DMTFA and DMAA exhibit better redox activity than do solvent molecules in the electrolytes, wherein DMTFA preferentially forms a LiF-rich uniform film and DMAA forms a polymer film on the surface of the electrodes. Besides this, the presence of the additives partially suppresses the decomposition of the electrolytes. The electrochemically stable films formed by the additives effectively protect the structure of the electrodes and improve battery performance at high voltage.