Preparation of Li4Ti5O12/carbon nanotubes composites and LiCoO2/Li4Ti5O12 full-cell with enhanced electrochemical performance for high-power lithium-ion batteries

Abstract

Through utilizing a facile solid-state sand-milling method, Li4Ti5O12/carbon nanotubes composites containing different quantities of carbon nanotubes were prepared. A series of characterizations detail the ways in which carbon nanotubes have affected grain morphology and electrochemical properties. It is clearly seen from scanning-electron-microscopy images that the carbon nanotubes have uniformly distributed around the Li4Ti5O12 particles and Li4Ti5O12/carbon nanotubes particles are smaller than that of pure Li4Ti5O12. The Li4Ti5O12/carbon nanotubes composite with 4.94 wt% carbon nanotubes (denoted as LTO-CNTs-2) exhibits excellent charge capacities at high C-rates (148.3 mAh g−1 at 20 C, 142.6 mAh g−1 at 30 C) and possesses an outstanding cycling performance with a charge capacity of 138.6 mAh g−1 and a capacity retention of 90.2% at 10 C after 900 cycles. Cyclic-voltammetry test indicates that LTO-CNTs-2 exhibits a larger lithium-ion diffusion coefficient (6.53 × 10−10 cm2 s−1) than that of pure Li4Ti5O12 (1.15 × 10−10 cm2 s−1). Electrochemical-impedance spectra curves also show that LTO-CNTs-2 delivers the smallest charge-transfer resistance (61.0 Ω) among all samples. The electrochemical performance of LiCoO2 (denoted as LCO)/pure Li4Ti5O12 and LCO/LTO-CNTs-2 full cells are investigated. The LCO/LTO-CNTs-2 full-cell exhibits a superior cycling performance with a discharge capacity as high as 143.9 mAh g−1 and a capacity loss of only 4.2% than that of LCO/pure Li4Ti5O12 full-cell at 5 C after 500 cycles, whose discharge capacity is 110.9 mAh g−1 with a capacity loss of 21.8%.