Li4Ti5O12, which is a high performance anode material for rechargeable Li-ion batteries, is crystallized directly via a novel continuous flow hydrothermal method using lithium ethoxide and titanium isopropoxide as reactants. Crystalline nanoparticles are obtained in a single step and in less than one minute, by mixing the reactants with superheated water in a continuous flow reactor at near- and supercritical conditions. The Li4Ti5O12 nanoparticles have an average crystallite size of 4.5 nm with a specific surface area of >= 230 m(2)/g. In-situ synchrotron powder X-ray diffraction measurements upon annealing of the nanocrystalline Li4Ti5O12 were performed in order to investigate the structural and microstructural changes from room temperature to 727 degrees C. The as-prepared crystalline nanoparticles show significant crystallographic strain, which is found to relax upon annealing above 500 degrees C, concurrent with crystallite growth. Electrochemical tests of the as-prepared Li4Ti5O12 and a sample annealed at 600 degrees C reveal that heat-treatment results in a significant improvement of the performance in terms of the specific capacity and the rate capability, and overall the annealed nanoparticles have excellent electrochemical properties. The origin of the crystallographic strain is discussed, and further optimization of this rapid, green and scalable synthesis approach is suggested. (C) 2011 The Electrochemical Society. [DOI: 10.1149/2.084202jes] All rights reserved.