Although aqueous asymmetric supercapacitors are promising technologies because of their high-energy density and enhanced safety, their voltage window is still limited by the narrow stability window of water. Redox reactions at suitable electrodes near the water splitting potential can increase the working potential. Here, we demonstrate a kinetic approach for expanding the voltage window of aqueous asymmetric supercapacitors using in situ activated MnO and VO electrodes. The underlying mechanism indicates a specific potential of ∼1 V vs Ag/AgCl for the oxidation of Mn-to-Mn at the positive electrode and ∼ -0.8 V vs Ag/AgCl for the reduction of V-to-V at the negative electrode, which limits oxygen and hydrogen evolution reactions, respectively. The as-fabricated aqueous asymmetric supercapacitor exhibited a working voltage of 2.2 V with a high-energy density of 42.7 Wh/kg and a power density of ∼1.1 kW/kg. This mechanism improves the voltage window and energy and power densities.

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The battery−supercapacitor hybrid (BSH) device has potential applications in energy storage and can be a remedy for low-power batteries and low-energy supercapacitors. Although several studies have investigated electrode materials (particularly for a battery-type anode material) and design for BSHs, the energy density and power density are insufficient (far from the levels required for practical applications). Herein, a hierarchical vanadium(IV) oxide on reduced graphene oxide (rGO@ VO 2 ) heterostructure as an anode and activated carbon on carbon cloth (AC@CC) as a cathode are proposed for fabricating an advanced BSH. The mixed valency of V ions inside the as-prepared VO 2 matrix (V 3+ and V 4+ ) facilitates redox reactions at a low potential, giving rise to rGO@VO 2 as a typical anode with a working potential of 0.01−3 V (vs Li/ Li + ). The sheet-on-sheet heterostructured rGO@VO 2 yields a high specific capacity of 1214 mAh g −1 at 0.1 A g −1 after 120 cycles, with a high rate capability and stability. The rGO@VO 2 //AC@CC BSH device exhibits a maximum gravimetric energy density of 126.7 Wh kg −1 and a maximum gravimetric power density of ∼10 000 W kg −1 within a working voltage range of 1−4 V. Moreover, it exhibits fast charging times of 5 and 834 s with energy densities of 15.6 and 82 Wh kg −1 , respectively.

An effective approach to alleviate the volume expansion of alloying material and magnify the capacity of sodium-ions batteries anode by anchoring the SnS nanoparticles densely on porous carbon nanotubes film.