Molecular Understanding of Charge Storage in MoS2 Supercapacitors with Ionic Liquids

Owing to high electrical conductivity and ability to reversibly host a variety of inserted ions, 2D metallic molybdenum disulfide (1T-MoS2) has demonstrated promising energy storage performance when used as a supercapacitor electrode. However, its charge storage mechanism is still not fully understood, in particular, how the interlayer spacing of 1T-MoS2 would affect its capacitive performance. In this work, molecular dynamics simulations of 1T-MoS2 with interlayer spacing ranging from 0.615 to 1.615 nm have been performed to investigate the resulting charge storage capacity in ionic liquids. Simulations reveal a camel-like capacitance-potential relation, and MoS2 with an interlayer spacing of 1.115 nm has the highest volumetric and gravimetric capacitance of 118 F cm(-3) and 42 F g(-1), respectively. Although ions in MoS2 with an interlayer spacing of 1.115 nm diffuse much faster than with interlayer spacings of 1.365 and 1.615 nm, the MoS2 with larger interlayer spacing has a much faster-charging process. Our analyses reveal that the ion number density and its charging speed, as well as ion motion paths, have significant impacts on the charging response. This work helps to understand how the interlayer spacing affects the interlayer ion structures and the capacitive performance of MoS2, which is important for revealing the charge storage mechanism and designing MoS2 supercapacitor.