Tuning the crystalline and electronic structure of ZrO2 via oxygen vacancies and nano-structuring for polysulfides conversion in lithium-sulfur batteries

The recent emergence of tetragonal phases zirconium dioxide (ZrO₂) with vacancies has generated significant interest as a highly efficient and stable electrocatalyst with potential applications in trapping polysulfides and facilitating rapid conversion in lithium-sulfur batteries (LSBs). However, the reduction of ZrO₂ is challenging, even under strong reducing atmospheres at high temperatures and pressures. Consequently, the limited presence of oxygen vacancies results in insufficient active sites and reaction interfaces, thereby hindering practical implementation. Herein, we successfully introduced abundant oxygen vacancies into ZrO₂ at the nanoscale with the help of carbon nanotubes (CNTs-OH) through hydrogen-etching at lower temperatures and pressures. The introduced oxygen vacancies on ZrO_2−x/CNTs-OH can effectively rearrange charge distribution, enhance sulfiphilicity and increase active sites, contributing to high ionic and electronic transfer kinetics, strong binding energy and low redox barriers between polysulfides and ZrO_2−x. These findings have been experimentally validated and supported by theory calculations. As a result, LSBs assembled with the ZrO_2−x/CNTs-OH modified separators demonstrate excellent rate performance, superior cycling stability, and ultra-high sulfur utilization. Especially, at high sulfur loading of 6 mg cm⁻², the area capacity is still up to 6.3 mA h cm⁻². This work provides valuable insights into the structural and functional optimization of electrocatalysts for batteries.