Sandwich-Like Heterostructures of MoS₂ /Graphene with Enlarged Interlayer Spacing and Enhanced Hydrophilicity as High-Performance Cathodes for Aqueous Zinc-Ion Batteries.

Abstract

Layered materials have great potential as cathodes for aqueous zinc-ion batteries (AZIBs) because of their facile 2D Zn²⁺ 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 MoS₂ gallery, which results in significantly enlarged MoS₂ interlayers (from 0.62 to 1.16 nm) and enhanced hydrophilicity. The sandwich-structured MoS₂ /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 MoS₂ /graphene nanocomposite exhibits exceptional high-rate capability (285.4 mA h g^-1 at 0.05 A g^-1 with 141.6 mA h g^-1 at 5 A g^-1 ) and long-term cycling stability (88.2% capacity retention after 1800 cycles). The superior Zn²⁺ 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-MoS₂ 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 MoS₂ /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.