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. A safe, controllable and affordable method using urea at mild temperatures to synthesise a series of sodium titanate samples with different levels of oxygen vacancies is reported. The formation of oxygen vacancies leads to the reduction of Ti4+ to Ti3+ ions in NTO, together with the formation of hydroxyl groups and a secondary phase, Na2Ti6O13.The urea‐treated samples showed superior electrochemical performance at high rates with respect to pristine NTO.