Nickel and cobalt sulfide-based nanostructured materials for electrochemical energy storage devices

Nickel and cobalt sulfides are considered to be effective electrode materials for high-performance electrochemical energy storage devices (EESDs) mainly due to their relatively abundant raw materials and considerable electrochemical reaction activity with relatively higher electrical conductivity, weaker metal-sulfur bonds and better thermal stability compared to their oxide counterparts. Thus, extensive effort has been devoted to the synthesis of nanostructured nickel and cobalt sulfides, and great promising progress has been achieved on their applications for efficient EESDs. In this review, we briefly introduce the most commonly used nickel and cobalt sulfides (e.g., CoS2, Co9S8, NiS, NiS2 and NiCo2S4) applied in various EESDs (e.g., battery-type supercapacitors, lithium/sodium-ion batteries, zinc-air batteries and lithium-sulfur batteries), and summarize a variety of nanostructures of nickel and cobalt sulfides developed in recent years and different methodologies for designing these nanostructures. Besides, nickel and cobalt sulfide-based composites combining the functions and advantages from carbon materials, conductive polymers or metal compounds are as well detailedly elaborated with considerable interest as active electrodes in EESDs. At last, we describe the existing problems and prospects of the nickel and cobalt sulfides as electrode materials in EESDs. More work should be dedicated to helping us make good use of nickel and cobalt sulfide-based electrode materials for EESDs in the near future.