Encapsulating NiS nanocrystal into nitrogen-doped carbon framework for high performance sodium/potassium-ion storage

Potassium-ion-battery (PIB) and sodium-ion-battery (SIB) have been considered as next-generation energy storage devices due to their low-cost and abundant resource. The main challenge lies in the lack of novel electrodes to accommodate the large-size K/Na-ions. Herein, a facile solvothermal method coupled with a polydopamine coating and post-annealing strategy is developed to synthesize unique box-like NiS@C. NiS particles are encapsulated in nitrogen-doped carbon cages via the Ni-N bond, presenting excellent sodium/potassium-ion storage performances. The coexistence of nitrogen doped carbon, as well as the chemical bond between NiS and carbon endows the composite with highly conductive network and fast ionic diffusion channels, exhibiting excellent rate capability. The superior cyclic stability can be attributable to the stronger affinity of N-doped carbon to NiS and discharge products, which has been further demonstrated through first-principles density functional theory (DFT) simulations. NiS@C delivers a high Na-ion-storage capacity of 632 mAh g(-1) at 5 A g(-1) over 2000 cycles. A stable K-ion storage capacity of 171 mAh g(-1) can be retained at 1 A g(-1) after 300 cycles. These findings suggest box-like NiS@C is a promising anode candidate for alkali-ion batteries. Present synthetic approach could be extended to other functional electrode materials for energy-storage applications.