Effects of carbon source and carbon content on electrochemical performances of Li4Ti5O12/C prepared by one-step solid-state reaction

Li4Ti5O12/C composites were synthesized by one-step solid-state reaction method using four commonly used organic compounds or organic polymers as carbon source, i.e., polyacrylate acid (PAA), citric acid (CA), maleic acid (MA) and polyvinyl alcohol (PVA). The physical characteristics of Li4Ti5O12/C composites were investigated by X-ray diffraction, electron microscopy, Raman spectroscopy, particle size distribution and thermogravimetry-derivative thermogravimetry techniques. Their electrochemical properties were characterized by cyclic voltammograms, electrochemical impedance spectra, constant current charge-discharge and rate charge-discharge. These analyses indicated that the carbon source and carbon content have a great effect on the physical and electrochemical performances of Li4Ti5O12/C composites. An ideal carbon source and appropriate carbon content effectively improved the electrical contact between the Li4Ti5O12 particles, which enhanced the discharge capacity and rate capability of Li4Ti5O12/C composites. PAA was the best carbon source for the synthesis of Li4Ti5O12/C composites. When the carbon content was 3.49 wt.% (LiOH center dot H2O/PAA molar ratio of 1), as-prepared Li4Ti5O12/C showed the maximum discharge capacity. At 0.2 C. initial capacity of the optimized sample was 168.6 mAh g(-1) with capacity loss of 2.8% after 50 cycles. At 8 and 10 C, it showed discharge capacities of 143.5 and 132.7 mAh g(-1), with capacity loss of 8.7 and 9.9% after 50 cycles, respectively. (C) 2011 Elsevier Ltd. All rights reserved.