An improved battery-supercapacitor-hybrid by electrochemically deposition of Anthraquinone-2-sulfonate/NiMn-layered double hydroxide on a 3D exfoliated graphite

Improving both the specific energy and power of a battery supercapacitor hybrid system was achieved by incorporating the redox-active anthraquinone-2-sulfonate (AQS) into NiMn-layered double hydroxide (NM-LDH) deposited on an exfoliated graphite current collector. Both processes, i.e., deposition of NM-LDH on a foam-like exfoliated graphite current collector and the doping of AQS were carried out electrochemically. Each of the components in this tertiary system plays an important role. The exfoliated graphite provides high conductivity and adds to energy storage through double-layer capacitance. The NM-LDH is the major faradaic component, whereas the AQS adds also to the faradaic energy storage as well as separates the NM-LDH 2D layers and increases the working potential window. The performance of the electrode was carefully characterized and optimized by adjusting the ratio between Ni and Mn in the LDH. The penetration of LDH and AQS was characterized using cross-section electron microscopy. The hybrid electrode exhibits a specific capacity of 612 mAh g⁻¹ at 2 mV s⁻¹ in 5 M KOH. Finally, a symmetric battery supercapacitor hybrid system was assembled using these electrodes and the device exhibited a specific capacity of 180 mAh g⁻¹. This device offers both high specific energy (77.8 Wh kg⁻¹) and power (34.9 kW kg⁻¹).