Surface Nitridation of Nano-sized Anatase TiO2 using Urea and Thiourea for Enhanced Electrochemical Performance in Lithium-ion Batteries

Given the critical importance of safety in lithium-ion batteries (LIBs), titanium dioxide (TiO₂) is widely regarded as a reliable material for the negative electrode. Anatase TiO₂ is a safe negative electrode material in LIBs, attributed to its high redox potential (1.5–1.8 V vs. Li/Li⁺), which exceeds that of commercially available graphite, alleviating the risk of lithium plating. In addition, TiO₂ has gained considerable attention as a cost-effective negative electrode material for LIBs, owing to its versatility in nano-sized forms. The use of nano-sized TiO₂ as an electrode-active material reduces the diffusion distance of Li⁺ ions. However, TiO₂ is adversely affected by its inherently low electronic conductivity, which hinders its rate performance. Herein, we investigated the surface treatment of commercially available TiO₂ nanoparticles with anatase structure using a heat-treatment process in the presence of urea or thiourea. Our objective was to leverage the eco-friendly nitridation of TiO₂ from the thermal decomposition of urea or thiourea, enhancing their electrochemical performance in lithium-ion batteries while minimizing environmental impact. Specifically, we employed an autogenic reactor (AGR) in a closed space to ensure an adequate reaction between NH₃ and TiO₂, preventing NH₃ from escaping into the external environment, as observed in open systems. Consequently, surface nitridation enhanced the overall electrochemical performance, including the rate capability, capacity retention, and initial Coulombic efficiency (ICE). Notably, a remarkable enhancement was observed for the thiourea-treated TiO₂. Compared to the pristine TiO₂, the thiourea-treated TiO₂ demonstrated a nearly threefold increase in capacity at 1.0 C and a nearly two-fold increase in capacity retention.