Enhancing the Performance of a Battery-Supercapacitor Hybrid Energy Device Through Narrowing the Capacitance Difference Between Two Electrodes via the Utilization of 2D MOF-Nanosheet-Derived Ni@Nitrogen-Doped-Carbon Core-Shell Rings as Both Negative and Positive Electrodes.

Abstract

Narrowing the capacitance gap between the positive and negative electrodes for the enhancement of the energy densities of battery-supercapacitor hybrid (BSH) devices is urgent and very important. Herein, a new strategy to synchronously improve the positive-negative system and reduce the capacitance discrepancies between two electrodes through the utilization of the same MOF-based precursors ([Ni(ATA)2(H2O)2](H2O)3) has been proposed. Nickel/nitrogen codoped carbon (Ni@NC) materials, serving as positive electrodes, deliver battery-type behavior with the enhancement of capacities, which are even superior to those of pristine carbon-based materials with large surface areas. Meanwhile, HCl-treated Ni@NC materials (named A-Ni@NC) are employed as negative electrodes within the potential window of -1 to 0 V and exhibit higher capacitances than that of the commercial activated carbon. With Ni@NC and A-Ni@NC as positive and negative electrodes in BSH devices, the as-fabricated cells display higher capacities and energy densities, more excellent cycling stability, and far superior capacity retention in comparison with those of Ni@NC//AC cells. These results clearly confirm that our strategy is successful and effective.