Titanium dioxide nanotubes modified with nickel oxide and nickel nanoparticles for improved polysulfide anchoring and redox kinetics in lithium–sulfur batteries

Abstract

This study systematically investigates and compares the roles of electronic conductivity, polysulfide chemisorption, and catalytic conversion in TiO₂ nanotube-based cathode hosts by evaluating three bifunctional additives: bare TiO₂ nanotubes, NiO-modified TiO₂ nanotubes (NiO/TiO₂), and Ni nanoparticle-modified TiO₂ nanotubes (Ni/TiO₂). Anatase phase TiO₂ nanotubes (∼18.3 nm) were synthesized via a hydrothermal method and integrated into carbon fibre paper to form TiO₂-CFP, NiO/TiO₂-CFP and Ni/TiO₂-CFP composite cathodes, which were evaluated at a high sulfur loading of 4 mg cm⁻². The cell with TiO₂-CFP exhibited moderate polysulfide adsorption but was constrained by poor conductivity and weak catalytic activity, delivering an initial capacity of 995.72 mA h g⁻¹ at 0.2C. The cell with NiO/TiO₂ improved chemisorption and redox conversion, achieving an initial capacity of 1196.4 mA h g⁻¹ at 0.2C. Among the tested electrodes, Ni/TiO₂-CFP delivered the best overall performance, exhibiting an initial specific capacity of 1285 mA h g⁻¹ at 0.2C and retaining ∼1095 mA h g⁻¹ after 100 cycles. Moreover, it showed excellent rate capability: 745.25 mA h g⁻¹, 659.03 mA h g⁻¹, and 381.52 mA h g⁻¹ at 0.5C, 1.0C and 2.0C, respectively, significantly outperforming cells with TiO₂-CFP and NiO/TiO₂-CFP. Ni/TiO₂-CFP further exhibited distinct charge–discharge plateaus with minimal polarization, the lowest charge transfer resistance (14 Ω) and the highest Li₂S nucleation capacity (746 mA h g⁻¹), confirming faster interfacial kinetics. These results establish that the metallic Ni modification of TiO₂ nanotubes most effectively balances polysulfide anchoring and catalytic conversion, providing a rational design pathway for high-loading Li–S battery cathodes.