Polysulfide Binding to Several Nanoscale Magnéli Phases Synthesized in Carbon for Long‐Life Lithium–Sulfur Battery Cathodes

Usman Zubair, Julia Amici, Carlotta Francia, David McNulty, Silvia Bodoardo, Colm O'Dwyer

In Li-S batteries, it is important to ensure efficient reversible conversion of sulfur to lithium polysulfide (LiPS). Shuttling effects caused by LiPS dissolution can lead to reduced performance and cycle life. While carbons rely on physical trapping of polysulfides, polar oxide surfaces can chemically bind LiPS to improve the stability of sulfur cathodes. We show a simple synthetic method allowing high sulfur loading into mesoporous carbon, pre-loaded with spatially localized nanoparticles of several Magnéli phase titanium oxide, TinO2n-1. This material simultaneously suppresses polysulfide shuttling phenomena by chemically binding Li polysulfides onto several Magnéli phase surfaces in a single cathode, and ensures physical confinement of sulfur and LiPS. The synergy between chemical immobilization of significant quantities of LiPS at the surface of several TinO2n-1 phases, and physical entrapment ensures Coulombically efficient, long cycle life, high capacity and high rate cathode. These cathodes function efficiently at low electrolyte to sulfur (E/S) ratios to provide high gravimetric and volumetric capacities in comparison with highly porous carbon counterparts. Assembled coin cells have an initial discharge capacity of 1100 mA h g-1 at 0.1 C, and maintain a reversible capacity of 520 mA h g-1 at 0.2 C for more than 500 cycles. Even at 1C, the cell loses only 0.06% per cycle for 1000 cycles with Coulombic efficiency close to 99%.