In this work series of Na0.7Co1-yMnyO2 (y = 0, 02, 03, 0.4, 0.6, 0.8) cathode materials were studied in terms of their structural, transport and electrochemical properties in Na/Na+/Na0.7Co1-yMnyO2 cells. The materials were synthesized by a high-temperature solid-state reaction. XRD measurements with Rietveld analysis confirmed presence of a single phase with P6(3)/mmc symmetry for all the obtained compositions, except for Na0.7Co0.6Mn0.4O2. Electrical conductivity shows metallic-type character for NaxCoO2 (x approximate to 0.7) and activated character for sodium cobaltate substituted with manganese. Electrical conductivity decreases with the increase of manganese content. Electrochemical studies performed for Na/Na+/Na(0.7+x)Cn(1-y)Mn(y)O(2) revealed changes in the character of discharge curve after replacement of Co ions with Mn ions. The most promising electrochemical performance was achieved for Na0.2Co0.2Mn0.3O2. Comprehensive studies of selected Na0.7Co0.7Mn0.3O2 composition (structural properties, discharge capacity at different current rates, cyclic voltammetry and impedance characteristic of cells) were conducted. (C) 2016 Elsevier B.V. All rights reserved.