Plasma-induced on-surface sulfur vacancies in NiCo2S4 enhance energy storage performance of supercapatteries

Vacancies have received considerable attentions in energy storage materials since they are able to generate more active defects, leading to enhanced conductivity and thus higher capability. Here, we provide a facile strategy to rapidly achieve sufficient sulphur vacancies, lattice distortion and changed charge-states of Ni/Co on the material surface layer in NiCo2S4 via low-temperature atmospheric pressure plasma. Both experimental results and DFT calculations have demonstrated that enhanced performances can be obtained with different amount of sulphur vacancies (S-vacancies), with optimal performance obtained at 30% S-vacancy. Moreover, the same trend of enhanced energy storage performance effects is found in comparison groups of varied Ni/Co atomic ratios (1:1, 2:1, 1:4, 4:1), suggesting a serviceability of this facile strategy, which only requires 30 seconds of processing. This paves a path towards high-performance supercapatteries using the simple plasma-based method.