Effect of carbon and N-doped carbon nanomaterials on the electrochemical performance of lithium titanate-based composites

Abstract

The composite nanomaterials based on hydrothermally synthesized Li4Ti5O12 and carbon nanotubes (CNTs) or carbon nanoflakes, including N-doped ones were prepared. The composites were investigated by X-ray powder diffraction, TEM, SEM, Raman spectroscopy, BET, dc-measurements, galvanostatic charge-discharge tests, cyclic voltammetry and electrochemical impedance spectroscopy. Carbon nanomaterial addition provides the formation of a highly conductive 3D network leading to a significant increase in the electrical conductivity and excellent electrochemical performance of the composites at high charge-discharge rates. At a current density of 6400 mA/g (~37C), the reversible discharge capacities of Li4Ti5O12 and its composites with CNTs and N-doped CNTs are 60, 92, and 96 mAh/g, respectively. They exhibit a remarkable long-term cycling stability: less than 0.034%, 0.013% and 0.005% loss per cycle over 500 cycles, respectively. The results obtained by Raman spectroscopy, BET, and electrochemical measurements suggest the interaction between polar fragments of the N-doped carbon nanomaterials and Li4Ti5O12 surface.