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.