These studies are devoted to electrical and electrochemical investigations of cobalt-doped manganese spinel. The studies of electrical conductivity and thermoelectric power in the wide temperature range (220-1090 K) in relation to oxygen nonstoichiometry together with the behaviour of the material in Li/Li+ /LixCoyMn2-yO4 cell enable to determine electronic defect structure of the LiCoyMn2-yO4 cathode material.