Facile synthesis of Ti₄O₇ on hollow carbon spheres with enhanced polysulfide binding for high-performance lithium-sulfur batteries

As the next generation of electrochemical energy storage devices, lithium sulfur (Li-S) batteries have many advantages such as high theoretical specific capacity (1675 mAh g^-1) and energy density (2600 kw h kg^-1), non-toxicity and low cost. However, the poor electrical conductivity of sulfur cathodes and the shuttling effect of lithium polysulfides during cycling strongly hinder the commercial application of Li-S batteries. In this study, Magnéli phase Ti₄O₇ nanoparticles were successfully prepared on the surface of hollow carbon spheres (HCS) through a carbothermal reduction reaction. The synthesized HCS@Ti₄O₇ with a mesoporous structure exhibited a uniform spherical morphology with a large specific surface area (512 m² g^-1) and the pore volume of 0.58 cm³ g^-1. The introduction of a polydopamine (PDA) layer during the preparation was confirmed to effectively inhibit the grain coarsening of Ti₄O₇. Moreover, the high content of sulfur loading (70%) did not affect the morphology of HCS@Ti₄O₇, which suggested its stable architecture. The assembled coin cells exhibited the superior reversible capacity of 1427 mAh g^-1 at 0.1C and favorable cycling stability from 1168 mAh g^-1 to 601 mAh g^-1 after 800 cycles at 0.5C with the capacity decay rate of only 0.06% per cycle. This excellent performance and stability were attributed to the strong chemical binding effects of Ti₄O₇ on lithium polysulfides and the stable morphology maintenance during cycling. This study provides a novel conception to design and synthesize nanocomposites between reduced metal oxides and carbon with uniform and stable mesoporous structures for high-performance Li-S batteries.