Ti4O7-Filled Nitrogen-Doped Carbon/Ti4O7 Double-Layer Spheres As Sulfur Host for Advanced Lithium Sulfur Batteries

Abstract

Holding the largest market share, Li-ion batteries have been optimized for the post two decades, although their capacity is limited by the energy density of intercalation materials to ~300 mA h g-1. New chemistries are being sought as the next-generation energy storage device with higher energy density and reduced cost. Lithium-sulfur batteries, with their environmental benignity, competitive cost and high theoretical energy density (~2600 Wh kg-1), were intensively investigated in recent years as a promising candidate to replace the current lithium ion batteries. In this study, nitrogen-doped hollow carbon spheres (NC) with conducting Magnéli-phase Ti4O7 as the filling agent were designed delicately by employing one-step approach to reduce TiO2 and carbonize polydopamine on pre-synthesized SiO2 spheres as the sacrificial template, followed by the infiltration of sulfur at 155oC. The properties and performance of the composite (NC/Ti4O7/S) were examined and evaluated as the cathode material for lithium sulfur (Li-S) batteries. It was demonstrated that the sulfur particles could be well contained in the NC/Ti4O7 shells with the sulfur content being ~70%, while the particle size and thickness of the carbon shell can be easily tuned by controlling the reactant concentration and reaction time. The assembled battery exhibited an initial capacity of ~938 mAh g-1 at 0.5 C with a high retention rate of 94.8% after 100 cycles, which corresponds to a capacity decay of 0.052% per cycle. The NC/Ti4O7/S composite provides a promising cathode material for future lithium sulfur batteries. Figure 1