Structure, morphology, and electrochemical characterization of anatase TiO2-coated TiNb2O7 for lithium-ion batteries

TiNb2O7 powders were prepared via the hydrothermal method followed by the post-calcination reaction. The assynthesized TiNb2O7 powders were further coated with different amounts of anatase TiO2, ranging from 4 mol% to 20 mol%. The deposited TiO2 particles could be easily observed on the surface of TiNb2O7 through HR-TEM. When the amounts of TiO2 on TiNb2O7 surface were increased from 0 mol% to 12 mol%, the capacity retention of TiNb2O7 batteries at 0.2C for 100 cycles was increased from 29.50 % to 63.06 %. Furthermore, the volume of generated gas from the batteries during cycling tests was decreased from 0.0035 mL to 0.0015 mL. The coating of anatase TiO2 avoided direct contact between TiNb2O7 and electrolyte to suppress the interface reaction and resolve the gassing problem of TiNb2O7. Therefore, the long-term cyclability of TiNb2O7-based batteries was improved via TiO2 coating on TiNb2O7. However, the excessive amounts of TiO2 coating on TiNb2O7 surface induced a significant increase in the charge transfer resistance of prepared batteries and the suppression of oxidation/reduction reactions of Nb5+/Nb4+ and Nb4+/Nb3+ in TiNb2O7, resulting in an unsatisfactory discharge capacity of TiNb2O7. The appropriate amounts of TiO2 coating could effectively improve the long-term cyclability of TiNb2O7 and preserve the discharge capacity of TiNb2O7.