Few-layered MoS2 with expanded interplanar spacing strongly encapsulated inside compact carbon spheres by C–S interaction as ultra-stable sodium-ion batteries anode

Abstract

Graphite-like metal sulfides, MoS2, is regarded as potential electrode of sodium-ion batteries (SIBs) because of its relatively large interplanar spacing (0.62 nm) and outstanding theoretical capacity (670 mA h g−1). However, original MoS2 electrode often suffered from shortened cycle life and poor rate capability owing to the serious volume change during sodium insertion/extraction and inferior inherent conductivity. Herein, MoS2/C compact spheres (MoS2/C CSs) with dense structure constituted by few-layered MoS2 and conductive carbon coating are successfully developed using a in-situ synthesis method. As anode of SIBs, MoS2/C CSs achieve a high capacity of 425 mA h g−1 after 200 cycles at 0.1 A g−1 with initial coulombic efficiency up to 84.8%. The reversible capacity is still maintained in 320 mA h g−1 after 400 cycles at 1 A g−1, which is three times of original MoS2 (110 mA h g−1). Besides, MoS2/C CSs also have considerable rate performance, reserving impressive capacity (310 mA h g−1) at 5.0 A g−1. The compact and conductive carbon coating effectively inhibits volume expansion and improves electrical conductivity, meanwhile, the few-layered MoS2 nanoflakes with ampliative interplanar spacing (0.73 nm) simplify the Na+ diffusion pathway and promote rapid diffusion of Na+. Furthermore, the C–S chemical bond tightly interlocks MoS2 and C, which guarantees the above mechanisms synergistically and continuously intensify the property of MoS2/C CSs anode. The above results are verified by ex-situ impedance, phase and morphology analysis.