Chemical Bonding and Physical Trapping of Sulfur in Mesoporous Magneli Ti sub(4)O sub(7) Microspheres for High-Performance Li-S Battery

Various host materials have been investigated to address the intrinsic drawbacks of lithium sulfur batteries, such as the low electronic conductivity of sulfur and inevitable decay in capacity during cycling. Besides the widely investigated carbonaceous materials, metal oxides have drawn much attention because they form strong chemical bonds with the soluble lithium polysulfides. Here, mesoporous Magneli Ti sub(4)O sub(7) microspheres are prepared via an in situ carbothermal reduction that exhibit interconnected mesopores (20.4 nm), large pore volume (0.39 cm super(3) g super(-1)), and high surface area (197.2 m super(2) g super(-1)). When the sulfur cathode is embedded in a matrix of mesoporous Magneli Ti sub(4)O sub(7) microspheres, it exhibits a superior reversible capacity of 1317.6 mA h g super(-1) at moderate current (C/10) and a low decay in capacity of 12% after 400 cycles at C/5. Strong chemical bonding of the lithium polysulfides to Ti sub(4)O sub(7), as well as effective physical trapping in the mesopores and voids in the matrix are considered responsible for the improved electrochemical performance. A mechanism of the physical and chemical interactions between mesoporous Magneli Ti sub(4)O sub(7) microspheres and sulfur is proposed based on systematic investigations. Mesoporous Magneli Ti sub(4)O sub(7) microspheres are synthesized by an in situ carbothermal reduction. The microspheres have a large mesopore diameter and high surface area, allowing up to 70 wt% sulfur loading. As host material of sulfur, composite microspheres show a high discharge capacity (1320 mA h g super(-1)) and long-term cyclability (12% fading after 400 cycles).