This work concerns amorphous poly(ethylene oxide) (PEO) rubbery electrolytes with new lithium salts, LiN(CF3CO)(2) and Li[CF3SO2N(CH2)(3)OCH3] (LiMPSA), which contain carbonyl or ether groups in their anions. Although these salts are markedly less conductive than LiN(CF3SO2)(2) or LiClO4, one of them (LiMPSA) yields a large fraction of a species that promotes lithium transport through back, diffusion under polarization in Li/PEO-LiX/Li symmetrical cells. Polarization experiments carried out on similar cells filled with PEO-LiX-KX, mixed-alkali electrolytes show that this species is a LIX2-complex of lower mobility than Lif in PEG. In turn, these experiments reveal that LiN(CF3CO)(2) yields a large fraction of LiX ion pairs more mobile than Li+ in PEG. These features, which are founded on theoretical models for polarization of PEO-LIX-KX electrolytes between lithium electrodes, agree with other properties (T-g elevation and conductivity) of the present systems.