Sandwich-Like Heterostructures of MoS /Graphene with Enlarged Interlayer Spacing and Enhanced Hydrophilicity As High-Performance Cathodes for Aqueous Zinc-Ion Batteries

Layered materials have great potential as cathodes for aqueous zinc-ion batteries (AZIBs) because of their facile 2D Zn transport channels; however, either low capacity or poor cycling stability limits their practical applications. Herein, two classical layered materials are innovatively combined by intercalating graphene into MoS gallery, which results in significantly enlarged MoS interlayers (from 0.62 to 1.16 nm) and enhanced hydrophilicity. The sandwich-structured MoS /graphene nanosheets self-assemble into a flower-like architecture that facilitates Zn-ion diffusion, promotes electrolyte infiltration, and ensures high structural stability. Therefore, this novel MoS /graphene nanocomposite exhibits exceptional high-rate capability (285.4 mA h g at 0.05 A g with 141.6 mA h g at 5 A g ) and long-term cycling stability (88.2% capacity retention after 1800 cycles). The superior Zn migration kinetics and desirable pseudocapacitive behaviors are confirmed by electrochemical measurements and density functional theory computations. The energy storage mechanism regarding the highly reversible phase transition between 2H- and 1T-MoS upon Zn-ion insertion/extraction is elucidated through ex situ investigations. As a proof of concept, a flexible quasi-solid-state zinc-ion battery employing the MoS /graphene cathode demonstrates great stability under different bending conditions. This study paves a new direction for the design and on-going development of 2D materials as high-performance cathodes for AZIBs.