Unraveling the "Gap-Filling" Mechanism of Multiple Charge Carriers in Aqueous Zn-MoS 2 Batteries.

The utilization rate of active sites in cathode materials for Zn-based batteries is a key factor determining the reversible capacities. However, a long-neglected issue of the strong electrostatic repulsions among divalent Zn 2+ in hosts inevitably causes the squander of some active sites (i.e., gap sites). Herein, we address this conundrum by unraveling the "gap-filling" mechanism of multiple charge carriers in aqueous Zn-MoS 2 batteries. The tailored MoS 2 /(reduced graphene quantum dots) hybrid features an ultra-large interlayer spacing (2.34 nm), superior electrical conductivity/hydrophilicity, and robust layered structure, demonstrating highly reversible NH 4 + /Zn 2+ /H + co-insertion/extraction chemistry in the 1 M ZnSO 4 +0.5 M (NH 4 ) 2 SO 4 aqueous electrolyte. The NH 4 + and H + ions can act as gap fillers to fully utilize the active sites and screen electrostatic interactions to accelerate the Zn 2+ diffusion. Thus, unprecedentedly high rate capability (439.5 and 104.3 mAh g -1 at 0.1 and 30 A g -1 , respectively) and ultra-long cycling life (8000 cycles) are achieved.