Theoretically, a solid redox pair of Li and S can be used for energy storage devices with high specific capacity and energy density using low-cost sulfur as the active material, making it one of the most promising candidates to replace conventional lithium ion batteries. However, the practical use of Li-S battery is hindered by persistent issues regarding the formation of soluble polysulfides (PS) during electrochemical cycles and their shuttling effect. In order to minimize the irreversible loss of the active material from the cathode and its subsequent deposition on the anode, a few noteworthy efforts have been reported, including insertion of a protection layer or addition of a functional agent that can adsorb PS on the cathode side.

In this work, we report conductive titanium(III) sulfide (Ti₂S₃) nanoparticles, synthesized using a simple radio frequency (RF)-powered induction thermal plasma method, as a bifunctional material to be used in the S cathode. Ti₂S₃ nanoparticles can provide electrical conductivity to the electrode with a smaller volume compared to conventional conducting agent carbon, while simultaneously having PS adsorption adequate to mitigate the diffusion of PS from the cathode and reduce accompanying problems. We prepared Ti₂S₃ nanoparticles agent with improved PS adsorptivity by applying simple defect chemistry. The synthesized Ti₂S₃ was first exposed to air to be oxidized and form S defect on its surface. The surface-oxidized Ti₂S₃ proposed in this work shows both sufficient adsorption property to PS and electronic conductivity, and thus enhance the cyclability and areal energy density of the Li-S battery. The cyclic performance of our Li-S cell was achieved up to ~800 mAh g_S^-1 even after 100 cycles at relatively high S loading of 3.0 mg_S cm^-2.