NiX Layered Double Hydroxide Nanowire Arrays (X = Co, Fe, and Mn) Coated with Nanometer-Thick Films of NiOOH and Then NiO as Electrodes for Supercapacitors

Owing to their low cost, transition metal layered double hydroxides (LDHs) have the potential to become the electrode material of choice for supercapacitors if they can provide good cyclic stability and high specific capacity. Herein, we introduce an approach for forming a high-quality, uniform thin film of nickel oxide (NiO) that can act as an auxiliary nickel oxyhydroxide (NiOOH) layer during redox cycling in an alkaline electrolyte. This approach leads to a core/double-shell NiCo-LDH/NiOOH/ALD-NiO electrode that exhibits an unprecedented specific capacity of 1420.2 C g–1 (even at 4 A g–1), retaining 93% of the capacity after 20,000 cycles. Even when combined with a simple anode of activated carbon, an asymmetric supercapacitor with this cathode provides an energy density of 72.6 W h kg–1 with exceptional durability (9.1% loss over 10,000 cycles). This extraordinary electrode when combined with an articulated anode in a supercapacitor is expected to meet or exceed the current energy density limit of lithium-ion batteries.