Lithium-metal polysulfide batteries with free-standing MoS_xC_y thin-film cathodes

Free-standing thin film electrodes hold huge promise for solid-state and micro batteries required by a range of portable electronic devices. However, for lithium-sulfur (Li–S) and lithium-metal polysulfide (Li-MS_x; M = Mo, V, Ti, etc.) batteries, the promising thin film electrodes are not possible yet because of low melting point of sulfur. Here, for the first time, we have developed amorphous molybdenum sulfide (MoS_x) – carbon (C_y) composite thin-films using a magnetron sputtering method with novel co-deposition of molybdenum metal and sulfur-carbon composite. The thin films were used as the free-standing cathode for Li-MS_x cells that demonstrates excellent cycling performance and rate capability without any shuttle effect. The Li-MoS_x cells exhibit a high areal-capacity of 115 μAh/cm² at the current density of 20 μA/cm², an excellent stability of 500 cycles and remarkable rate capability with no traces of shuttle effect. Density functional theory (DFT)-Molecular dynamics (MD) based calculations reveal the insertion of lithium via an optimal mix of conversion and intercalation reactions without breaking the base Mo-S_x structure, eliminating the shuttle effect, and producing stable cycling performance.