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

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.