Hierarchical NiCo2S4@NiO Core-Shell Heterostructures as Catalytic Cathode for Long-Life Li-O2 Batteries

The critical challenges of Li-O-2 batteries lie in sluggish oxygen redox kinetics and undesirable parasitic reactions during the oxygen reduction reaction and oxygen evolution reaction processes, inducing large overpotential and inferior cycle stability. Herein, an elaborately designed 3D hierarchical heterostructure comprising NiCo2S4@NiO core-shell arrays on conductive carbon paper is first reported as a freestanding cathode for Li-O-2 batteries. The unique hierarchical array structures can build up multidimensional channels for oxygen diffusion and electrolyte impregnation. A built-in interfacial potential between NiCo2S4 and NiO can drastically enhance interfacial charge transfer kinetics. According to density functional theory calculations, intrinsic LiO2-affinity characteristics of NiCo2S4 and NiO play an importantly synergistic role in promoting the formation of large peasecod-like Li2O2, conducive to construct a low-impedance Li2O2/cathode contact interface. As expected, Li-O-2 cells based on NiCo2S4@NiO electrode exhibit an improved overpotential of 0.88 V, a high discharge capacity of 10 050 mAh g(-1) at 200 mA g(-1), an excellent rate capability of 6150 mAh g(-1) at 1.0 A g(-1), and a long-term cycle stability under a restricted capacity of 1000 mAh g(-1) at 200 mA g(-1). Notably, the reported strategy about heterostructure accouplement may pave a new avenue for the effective electrocatalyst design for Li-O-2 batteries.