Beyond Intercalation-Based Supercapacitors: The Electrochemical Oxidation from Mn3O4 to Li4Mn5O12 In Li2SO4 Electrolyte

The difficulty of enlarging the voltage window for aqueous asymmetric supercapacitors seriously impedes the enhancement in energy density, thus affecting their practical applications. Herein, lithium-rich Li4Mn5O12 nanoflakes are firstly in situ synthesized on carbon cloth through the electrochemical oxidation of prefabricated Mn3O4 nanowalls in a traditional three-electrode cell using Li2SO4 as electrolyte. It is intriguingly found that the potential windows for the Mn3O4 and Li4Mn5O12 electrodes can be enlarged to 0–1.2 V (vs Hg/Hg2Cl2) with high specific capacitances of 527 and 627 F g−1 at 1 mA cm−2, respectively. The CV kinetic analysis reveals different charge storage mechanisms for the Mn3O4 and Li4Mn5O12 electrodes, major capacitances of which are identified as the surface capacitive contribution and diffusion-controlled contribution, respectively. Making the best of separate potential window of the Li4Mn5O12 cathode and activated carbon anode, the as-assembled aqueous asymmetric supercapacitor device exhibits a wide voltage window of 2.2 V with a large energy density of up to 78 Wh kg−1 at 295 W kg−1 as well as ideal cycle stability, significantly outstripping previously reported Mn-based supercapacitors. Therefore, the excellent energy storage property together with low cost enables the assembled aqueous asymmetric supercapacitors to become a highly potential candidate for more possible future applications.