Strong charge polarization effect enabled by surface oxidized titanium nitride for lithium-sulfur batteries.

The commercialization of high-energy-density and low-cost lithium-sulfur batteries has been severely impeded by capacity fading and electrochemical polarization. Here we report a strategy to entrap polysulfides and boost the cathodic redox kinetics by embedding the surface oxidized quantum-dot-size TiN (TiN-O) within the highly ordered mesoporous carbon matrix. While the carbon scaffold offers sufficient electrical contact to the insulate sulfur, benefiting the full usage of sulfur and physical confinement of polysulfides. The surface oxygen renders TiN-O with a strong charge polarization effect for polysulfides via S-O-Ti bond as verified experimentally and theoretically. The suppressed shuttle effect and high lithium ion diffusion coefficient (7.9 × 10⁻⁸ cm² s⁻¹) lead to a high capacity of 1264 mA h g⁻¹ at 0.2 C with a negligible capacity fading rate of 0.06% per cycle. Additionally, TiN-O based prototype soft-package cells also exhibit excellent cycling stability with flexibility, demonstrating their potential for practical applications. Capacity fading and electrochemical polarization pose barriers to the commercial use of lithium-sulfur batteries. Here the authors show improved charge polarization and electrochemical performance in a surface oxidized quantum-dot-size titanium nitride embedded within a highly ordered mesoporous carbon matrix. [ABSTRACT FROM AUTHOR]