A nanocrystalline Li4Ti5O12-TiO2 duplex phase has been synthesized by a simple basic molten salt process (BMSP) using an eutectic mixture of LiNO3-LiOH-Li2O2 at 400-500 degrees C. The microstructure and morphology of the Li4Ti5O12-TiO2 product are characterized by means of X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and transmission electron microscopy (TEM). The sample prepared by heat-treating at 300 degrees C for 3 h (S-1) reveals dense agglomerates of ultra-fine nanocrystalline Li4Ti5O12; with heat treatment at 400 degrees C for 3 h (S-2), there is a duplex crystallite size (fine < 10 nm, and coarse > 20 nm) of Li4Ti5O12-TiO2; at 500 degrees C for 3 h (S-3), a much coarser and less-dense distribution of lithium titanate (crystallite size similar to 15-30 nm) is observed. According to the results of electrochemical testing, the S-2 sample shows initial discharge capacities of 193 mAh g(-1) at 0.2 C, 168 mAh g(-1) at 0.5 C. 146 mAh g(-1) at 1 C, 135 mAh g(-1) at 2 C, and 117 mAh g(-1) at 5 C. After 100 cycles, the discharge capacity is 138 mAh g(-1) at 1 C with a capacity retention of 95%. The S-2 sample yields the best electrochemical performance in terms of charge-discharge capacity and rate capability compared with other samples. Its superior electrochemical performance can be mainly attributed to the duplex crystallite structure, composed of fine (<10 nm) and coarse (>20) nm nanoparticles, where lithium ions can be stored within the grain boundary interfaces between the spinel Li4Ti5O12 and the anatase TiO2. (C) 2010 Elsevier B.V. All rights reserved.