As a basic study for cathode materials of {{{{ { {LiMn }_{2 }O }_{4 } }}-based lithium-ion secondary batteries Li({{{{ { { { {Mn }_{1-$delta$ }Nb }_{$delta$} )}_{2 }O }_{4 } }} ($delta$=0.05, 0.1, 0.2) materials which Nb is substituted for Mn were synthesized by the solid state reaction at 80$0^{circ}C$ and 110$0^{circ}C$ respectively. The second phase {{{{ { LiNbO}_{3 } }} appeared above $delta$=0.1 As the result of im-pedance analysis as the amount of substituted Nb increased the resistivity of grain boundary increased greatly. Compared to undoped-{{{{ { {LiMn }_{2 }O }_{4 } }} the electrical conductivity of Li({{{{ { { { {Mn }_{1-$delta$ }Nb }_{$delta$} )}_{2 }O }_{4 } }} decreased slightly but is charging capacity and potential plateau increased.