Oxygen vacancy-rich black TiO2 nanoparticles as a highly efficient catalyst for Li–O2 batteries

Abstract

Lithium-oxygen batteries (LOBs) have been extensively studied as an attractive secondary battery due to their ultra-high energy density. However, its high charging voltage, poor cycle stability, and low rate performance make its practical applications very limited. Since the positive electrode is the main reaction site of LOBs, improving the structure and catalytic activity of the cathode catalyst is the key method to improve the electrochemical performance. In this work, colored titanium dioxide nanoparticles were synthesized by calcination in argon. Raman and XPS confirmed the existence of more oxygen vacancies and Ti3+ in black TiO2 than gray one. HRTEM analysis also reveals the defective layers of 2–3 nm on the TiO2 surface. Due to the high electrical conductivity and good catalytic activity promoted by oxygen vacancies and Ti3+ ions, the black TiO2-based cathodes have good electrochemical activity and enhanced cycling stability for LOBs. Compared with the gray TiO2 (4.3 V), the black TiO2 nanoparticles show a low overpotential with the charge voltage of 3.7 V. The charging voltage significantly reduced approximately 600 mV, which reduces the battery's side reactions and polarization, and thus enhances the cycling performance of the battery. When the cut-off capacity is 500 mAh g−1, it can run for 108 cycles without significant change in terminal voltage, indicating that black TiO2 is an efficient catalyst for LOBs.