The charge/discharge, electrochemical impedance, cyclic voltammogram, and cycling behaviors of crystalline KxMnO2-nH(2)O as cathode material for supercapacitors in Li2SO4, Na2SO4, and K2SO4 electrolytes were compared. The different power and cycling performance of KxMnO2-nH(2)O during charge/discharge in the three electrolytes were elucidated by analyzing its composition and structure evolution. Compared with the Li2SO4 and Na2SO4 electrolytes, the highest ionic conductivity of K2SO4 electrolyte, the fastest charge-transfer process and slightest structural evolution of K,KxMnO2.nH(2)O during charge/discharge in the K2SO4 electrolyte lead to a superior power and cycling behavior for supercapacitor application. (C) 2012 Elsevier B.V. All rights reserved.