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°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°C for 3h (S-1) reveals dense agglomerates of ultra-fine nanocrystalline Li4Ti5O12; with heat treatment at 400°C for 3h (S-2), there is a duplex crystallite size (fine<10nm, and coarse>20nm) of Li4Ti5O12–TiO2; at 500°C for 3h (S-3), a much coarser and less-dense distribution of lithium titanate (crystallite size ∼15–30nm) is observed. According to the results of electrochemical testing, the S-2 sample shows initial discharge capacities of 193mAhg−1 at 0.2C, 168mAhg−1 at 0.5C, 146mAhg−1 at 1C, 135mAhg−1 at 2C, and 117mAhg−1 at 5C. After 100 cycles, the discharge capacity is 138mAhg−1 at 1C 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 (<10nm) and coarse (>20) nm nanoparticles, where lithium ions can be stored within the grain boundary interfaces between the spinel Li4Ti5O12 and the anatase TiO2.