The layered sodium manganese oxides Na0.7MnO2.05 material was synthesized using Na2CO3 and Mn3O4 precursors via a solvothermal method at different temperatures. The X-ray diffraction (XRD) shows that the Na0.7MnO2.05 sample has a high crystallinity with hexagonal crystal system. The electrochemical performance was characterized by cyclic voltammetry (CV), impedance measurements and galvanostatic charge discharge tests in symmetric Na-ion supercapacitors with 1 mol L-1 Na2SO4 solution as electrolyte. The Na0.7MnO2.05 material shows a high specific capacity of about 162.5 F g(-1) at a current density of 50 mA g(-1) and a high coulombic efficiency approaching 100%. Even at a current density of 200 mA g-1, the discharge capacity of the material can reach to 146 F g(-1). This electrode material holds great promise for practical applications. (C) 2015 Elsevier B.V. All rights reserved.