A phase transition from spinel Mn3O4 to layered birnessite has been reported through electrochemically induced activation in aqueous electrolyte for high performance supercapacitor, battery and water splitting applications. Here, Li2SO4, MgSO4 and K2SO4 aqueous electrolytes were used for the activation of Mn3O4 electrode to investigate the effect of electrolyte cation on the electrochemical activation. The Mn3O4 electrode exhibited different activated results in the three electrolytes, including the efficiency of phase transition, morphology of resulting birnessite and capacitive performance of the activated electrode. The cations affect the proceeding of H+ insertion or the peeling-off of birnessite nanosheets during the phase transition process, resulting in the formation of nanosheet materials with different lateral dimensions. Effect of electrolyte cation on the electrochemical behavior of nanosheets electrode is further investigated. The nanosheets electrode activated in K2SO4 exhibits capable capacitive behavior with reasonable specific capacitance and cycling stability. Understanding how different cations affect the phase transition of Mn3O4 together with its capacitive performance will conduce to the development of manganese oxide electrode systems with high performance.