Nitrogen-Doped TiO2- x(B)/MXene Heterostructures for Expediting Sulfur Redox Kinetics and Suppressing Lithium Dendrites.

Abstract

Practical application of lithium-sulfur (Li-S) batteries is severely impeded by the random shuttling of soluble lithium polysulfides (LiPSs), sluggish sulfur redox kinetics, and uncontrollable growth of lithium dendrites, particularly under high sulfur loading and lean electrolyte conditions. Here, nitrogen-doped bronze-phase TiO2(B) nanosheets with oxygen vacancies (OVs) grown in situ on MXenes layers (N-TiO2- x(B)-MXenes) as multifunctional interlayers are designed. The N-TiO2- x(B)-MXenes show reduced bandgap of 1.10eV and high LiPSs adsorption-conversion-nucleation-decomposition efficiency, leading to remarkably enhanced sulfur redox kinetics. Moreover, they also have lithiophilic nature that can effectively suppress dendrites growth. The cell based on the N-TiO2- x(B)-MXenes interlayer under sulfur loading of 2.5mg cm-2 delivers superior cycling performance with a high specific capacity of 690.7 mAh g-1 over 600 cycles at 1.0 C. It still has a notable areal capacity of 6.15 mAh cm-2 after 50 cycles even under a high sulfur loading of 7.2mg cm-2 and a low electrolyte-to-sulfur (E/S) ratio of 6.4 µL mg-1. The Li-symmetrical battery with the N-TiO2- x(B)-MXenes interlayer showcases a low over-potential fluctuation with 21.0mV throughout continuous lithium plating/stripping for 1000h. This work offers valuable insights into the manipulation of defects and heterostructures to achieve high-energy Li-S batteries.