Outstanding Catalytic Effects of 1T'-MoTe2 Quantum Dots@3D Graphene in Shuttle-Free Li-S Batteries.

Abstract

It is still challenging to develop sulfur electrodes for Li-S batteries with high electrical conductivity and fast kinetics, as well as efficient suppression of the shuttling effect of lithium polysulfides. To address such issues, herein, polar MoTe2 with different phases (2H, 1T, and 1T') were deeply investigated by density functional theory calculations, suggesting that the 1T'-MoTe2 displays concentrated density of states (DOS) near the Fermi level with high conductivity. By optimization of the synthesis, 1T'-MoTe2 quantum dots decorated three-dimensional graphene (MTQ@3DG) was prepared to overcome these issues, and it accomplished exceptional performance in Li-S batteries. Owing to the chemisorption and high catalytic effect of 1T'-MoTe2 quantum dots, MTQ@3DG/S exhibits highly reversible discharge capacity of 1310.1 mAh g-1 at 0.2 C with 0.026% capacity fade rate per cycle over 600 cycles. The adsorption calculation demonstrates that the conversion of Li2S2 to Li2S is the rate-limiting step where the Gibbs free energies are 1.07 eV for graphene and 0.97 eV for 1T'-MoTe2, revealing the importance of 1T'-MoTe2. Furthermore, in situ Raman spectroscopy investigation proved the suppression of the shuttle effect of LiPSs in MTQ@3DG/S cells during the cycle.