Two-dimensional molybdenum disulfide (MoS2) has been extensively investigated in applications for lithium (Li) storage material owing to its high theoretical capacity of ~670 mAh/g, while its low ionic and electrical conductivities and poor reversibility have tackled further development for battery applications. To mitigate these challenges, here we show incorporation of heteroatom with the same chalcogen group, selenium (Se), to MoS2 and design tubular structure by coating on multi-walled carbon nanotube (MWCNT). The molybdenum sulfide selenide (MoSSe) shell on MWCNT structure was synthesized from one-pot hydrothermal reaction. Transmission electron microscopy (TEM) images exhibit bi- or tri-layers of MoSSe shell that coaxially coat the sidewall of MWCNT. Electron energy loss spectroscopy (EELS) analysis reveals 1: 0.7: 1 atomic ratio of Mo: S: Se for MoSSe shell. Notably, the presence of Se distorts total lattice structure, thus increasing the interlayer space to 6.6 Å, which is 0.4 Å larger than Se-free MoS2. To evaluate electrochemical storage capability, few-layer MoSSe/MWCNT composites were prepared to binder-free and three-dimensional (3-D) structural electrode. The specific capacity for MoSSe/MWCNT electrode coupled with a counterpart of metallic Li electrode is ~1,900 mAh/g at a current density of 100 mA/g and ~95% of Coulombic efficiency is delivered. The 3-D electrode structure and few-layer MoSSe on MWCNT may allow for short diffusion distance of Li+ ion and fast electron transfer, respectively. The galvanostatic cell performance with MoSSe/CNT electrode was also compared with the similar structure of MoS2/MWCNT electrode. With increasing a current density to 1,200 mA/g, the capacity of MoSSe/MWNT is a twofold increase in that of MoS2/MWCNT, which indicates intrinsically higher lithium storage capability of MoSSe than MoS2. The decreasing bandgap of MoS2 by addition of Se can enhance electrical conductivity. In addition, the distorting atomic structure may signify the mobility of Li+ ion inside MoSSe shell. The few-layer MoSSe with MWCNT electrode is stably cycled in the measured 30 cycles, which is distinct from poor capacity retention of MoS2/MWCNT electrode.
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