Surface and defect engineered polar titanium dioxide nanotubes as an effective polysulfide host for high-performance Li-S batteries

In this work, the surface structure of as received and ball milled (BM) titanium dioxide (TiO2) was modified via a simple hydrothermal method to create nanotubes (TiO2 NTs and TiO2 BM NTs) and subsequently chemically reduced to introduce widespread oxygen vacancy defects (TiO2-x NTs and TiO2-x BM NTs). The high surface area, innate polar nature, and high conductivity of TiO2 NTs allow the host material to effectively trap the lithium polysulfides both physically and chemically and improve the redox kinetics of lithium polysulfides. Chemical reduction acts to further improve the performance of the NTs by increasing the amount of polysulfides that can be adsorbed and by further increasing the conductivity of the material. Galvanostatic charge-discharge cycling testing revealed good performance for all four of the tested cathode hosts, with the best performance being achieved by TiO2 BM NTs and TiO2-x NTs, with the former delivering an initial discharge capacity of 1204.72 mAh g-1 at 0.1 C and 767.69 mAh g-1 at 3 C and the latter delivering an initial discharge capacity of 1005.24 mAh g-1 at 0.1 C, 353.7 mAh g-1 at 3 C, and a decay rate of -0.68% per cycle over the first 300 cycles at 3 C.