An electro-activated bimetallic zinc-nickel hydroxide cathode for supercapacitor with super-long 140,000 cycle durability

Inorganic double hydroxides are promising battery-type cathode materials for supercapacitors. Currently, the main limitation for the practical application of double hydroxides is their poor cyclic stability, which is originating from the relatively low electrical conductivity and irreversible phase transition. Herein, bimetallic zinc-nickel double hydroxide nanosheet arrays (ZNDH NSAs) are designed and assembled into an asymmetric supercapacitor with ultralong cyclic stability, demonstrating enormous potential as a high-performance cathode in practical applications. This bimetallic hydroxide is first spontaneously crystallized into two-dimensional nanosheets with thickness of ~10 nm, which ensure highly active sites for surface reactions. Then the as-prepared materials are further modified over an electro-activation process, which, as demonstrated by combining experimental evidence and computational simulation, leads to more defective oxygen, enlarged lattice, and reduced Ni valence, synergistically improving the charge transfer kinetics. Moreover, the introduction of Zn effectively suppresses phase transformation during ultralong cyclic stability tests and leads to improved conductivity of Zn-Ni hydroxide system. Therefore, the electro-activated ZNDH NSAs electrode exhibits an excellent capacitance of 6834 mF cm⁻² at 3 mA cm⁻², and superior rate capability. The assembled supercapacitor delivers a record high cycling stability with zero capacitive loss after 140,000 cycles. To our knowledge, it is the best cycling performance for asymmetric supercapacitors.