This paper presents a novel approach to an explanation of apparently different characters of the discharge/charge curve in LixCoO2 (monotonous curve in large range of lithium content) and NaxCoO2 (-) (y) systems (step-like curve). Comprehensive experimental and theoretical studies on crystallographic, electronic and electrical transport properties of the LixCoO2 battery cathode material are reported. In the case of NaxCoO2 (- y) it was evidenced that the origin of the observed step-like character of the discharge/charge curve of NaxCoO2 (-) (y) is due to the specific features of the electronic structure, arisen from the presence of the oxygen vacancies and sodium ordering. (C) 2014 Elsevier B.V. All rights reserved.