Promoted lithium polysulfide conversion and immobilization by conductive titanium oxynitride-carbon architecture design for advanced lithium–sulfur batteries

Abstract

In this work, a multifunctional oxygen deficient titanium oxynitride skeleton featuring a Co-metal-decorated three-dimensional ordered macroporous (3DOM) structure embedded with N-doped carbon nanotubes (Co@TiO_xN_y/N-CNTs) is fabricated as a sulfur host for lithium–sulfur (Li–S) batteries. The unique 3DOM framework provides abundant space for sulfur accommodation and effective pathways for electrolyte infiltration. The robust titanium oxynitride skeleton also ensures good structural integrity during the repeated charge/discharge cycling. Meanwhile, the introduction of oxygen defects not only improves the intrinsic conductivity of the TiO₂ skeleton but also enhances its capability for lithium polysulfide (LiPS) trapping. The N-CNTs embedded in the macroporous framework form an ultra-high conductive network and also provide rich micropores for sulfur distribution and physical confinement. The highly dispersed Co nanoparticles uniformly anchored on TiO_xN_y and N-CNTs act as electrocatalysts promoting the conversion of LiPSs. Attributed to these features, the Co@TiO_xN_y/N-CNTs/S electrode presents good rate capability and excellent cycling performance. Even under a sulfur loading of 6.34 mg cm⁻² and a low electrolyte to sulfur ratio (E/S = 8 μL mg⁻¹), a high area capacity of 5.05 mA h cm⁻² can be achieved after 50 cycles. The flexible pouch cell also delivers an impressive discharge capacity of 972 mA h g⁻¹ after 100 cycles under a sulfur loading of 4 mg cm⁻². This work offers a rational strategy for the design of advanced sulfur cathodes for Li–S batteries.