Lithium salts. such as LiBF4, LiClO4, and LiPF6, were added to the "single-ion" solid polymer electrolyte poly[lithium bis { endomethyl-oligo(oxyethylene)oxy}oligo(oxyethylene)oxyaluminate] in which Li+ is the only mobile ion, to adjust the transport number from t(+) = 1 (t(-) = 0: single-ionic) to t(+) approximate to t(-) approximate to 0.5. When LiBF4 was used, the average transport number was found to deviate little over a wide salt concentration range. This characteristic meets a requirement for Li/polyaniline(n+)(BF4-)(n) batteries in which the salt concentration fluctuates with the ingress/egress of Li+ and X-during the charging/discharing processes. A Li/polyaniline(n+)(BF4-)(n) cell using this transport-number adjusted electrolyte exhibited a distinct discharge plateau at a reasonably high voltage and excellent cycle stability.