Nickel disulfide nanosheet as promising cathode electrocatalyst for long-life lithium–oxygen batteries

Lithium–oxygen batteries (LOBs) are considered as next-generation energy storage systems owing to their high energy densities. In order to achieve high-performance LOBs, it is necessary to develop efficient electrocatalysts that exhibit reversible formation and decomposition of discharge products on the oxygen-electrode side. In this study, single-crystalline NiS₂ nanosheets (NiS₂-NSs) are fabricated as an efficient electrocatalyst in an oxygen-electrode for high-performance LOBs. Ni(OH)₂-NSs are prepared through a hydrothermal reaction and subsequently reacted with sulfur by a solid/gas phase reaction process to form NiS₂-NSs. As an electrocatalyst in an oxygen-electrode, the single-crystalline NiS₂-NSs can reversibly form and decompose the discharge products during the discharging and charging processes, respectively. In particular, the NiS₂-NSs more effectively decompose the discharge products compared to the Ni(OH)₂-NSs owing to its high affinity to oxygenated species. In addition, the NiS₂-NSs exhibit a long-term cyclability over 300 cycles at a current density of 1000 mA g⁻¹ with a cut-off capacity of 1000 mA h g⁻¹. Moreover, NiS₂-NSs without conducting agent exhibit an electrocatalytic activity and its LOB performance can be further maximized through addition of a redox mediator.