The influence of the electrode potential on the electric conductivity of polymer complexes of nickel with salen-type ligands (where salen is N,N′-ethylene-bis(salicylideneimine)) differing by substituents in ligand′s benzene ring is studied in the course of measuring cyclic voltammograms. The highest electron conductivity is observed for the film of poly[N,N′-ethylene-bis(3-methoxysalicylideneiminato) nickel(II)] (poly[Ni(CH3OSalen)]) in 1 M LiPF6 solution in the ethylene carbonate-diethylcarbonate mixture (EC: DEC = 1: 1). Poly[N,N′-ethylene-bis(3-methyl-salicyleneiminato) nickel(II)] (or poly[Ni(CH3Salen)]) was found to have the widest potential range of electronic conductivity. Conditions are selected for synthesizing films from solutions of the corresponding monomers in 1 M LiPF6 EC: DEC electrolyte. The electrode potential intervals suitable for the use of poly[Ni(CH3Salen)] as the buffer interlayer between the aluminum substrate and the cathode mass in lithium-ion batteries for protecting the latter against overcharge are found.