Surface Engineering Strategy Using Urea To Improve the Rate Performance of Na₂Ti₃O₇ in Na-Ion Batteries

Na₂Ti₃O₇ (NTO) is considered a promising anode material for Na-ion batteries due to its layered structure with an open framework and low and safe average operating voltage of 0.3 V vs. Na⁺/Na. However, its poor electronic conductivity needs to be addressed to make this material attractive for practical applications among other anode choices. Here, we report a safe, controllable and affordable method using urea that significantly improves the rate performance of NTO by producing surface defects such as oxygen vacancies and hydroxyl groups, and the secondary phase Na₂Ti₆O₁₃. The enhanced electrochemical performance agrees with the higher Na⁺ ion diffusion coefficient, higher charge carrier density and reduced bandgap observed in these samples, without the need of nanosizing and/or complex synthetic strategies. A comprehensive study using a combination of diffraction, microscopic, spectroscopic and electrochemical techniques supported by computational studies based on DFT calculations, was carried out to understand the effects of this treatment on the surface, chemistry and electronic and charge storage properties of NTO. This study underscores the benefits of using urea as a strategy for enhancing the charge storage properties of NTO and thus, unfolding the potential of this material in practical energy storage applications.