Design of ultra-thick graphene-molybdenum disulfide electrodes to reduce volume expansion and capacity fading by first principles

Abstract

The shuttling of polysulfide intermediates and volume distortion during cycling make it challenging for the applications of MoS2 at high current densities without capacity fading. In order to improve the cycle life and rate capability of lithium-ion batteries, introducing a porous matrix is a viable strategy. Here, MoS2 with 3D porous graphene prepared by low-temperature hydrothermal (160 °C) and low-energy ultrasound-assisted (40 W for 120 s) methods shows no impurities, large layer thickness (0.94 nm, 54 % increase) and no bare MoS2, resulting in smaller volume expansion (34 % in Li4MoS2), higher lithium stability (0.66 eV of adsorption energy) and more convenient ion transport channels. The first-principles calculations show that more lithium can be inserted without destroying the layered structure by forming a lithium metal layer between the MoS2 layers. The encapsulation of graphene not only hinders the shuttle effect of sulfur, but also improves the adsorption energy of lithium atoms in the electrode. In addition, electrochemical analysis shows that the clear drop in charge transfer resistance (Rct) in the first 300 cycles also indicates the improvement of the reaction pathway by graphene. As a result, the as-prepared rGO/MoS2 still maintains a specific capacity of 1008 mAh·g−1 with a very low capacity decay rate (0.03 % per cycle) at a current density of 1 A·g−1 after 500 cycles as an electrode material for lithium-ion batteries.