Conductivity enhancement of polymer electrolytes by addition of cascade nitriles and polarization behavior of lithium electrode in the electrolytes

Conductivity enhancement of polyacrylonitrile (PAN)-based electrolytes was achieved by the addition of the cascade compounds with one amino and three nitrile (tris[(cyanoethoxy)methyl]-aminomethane (TCEMAM)) or four nitrile (tetrakis[(cyanoethoxy)methyl]-methane (TCEMM)) groups to the electrolytes. The conductivity of the electrolytes with the cascade nitrile compounds was about one order of magnitude higher than that of the additive-free one. X-ray diffraction, DSC, and 7Li NMR measurements of the electrolytes suggested that the additives acted as a dissolution enhancer for the lithium (Li) salt in the electrolytes. Complex formation between the Li ions and the cascade nitrile compounds was also suggested by the NMR results. The coupling between the Li ions and the nitrile groups in the PAN side chains was weakened by the complex formation. The cascade nitrile compounds in the PAN-based electrolytes act as a dissolution enhancer of Li salt and a decoupler between the Li ions and the PAN chains. Therefore, they enhanced the conductivity of the PAN-based electrolytes with them. Polarization behavior of a Li electrode was also investigated in the additive-free electrolyte and the electrolytes with the additives. The exchange current density of the Li electrode in the electrolyte with the additives was about two orders of magnitude higher than that in the additive-free one.