The authors prepared uniformly shaped WO2.72 nanowire bundles using the solvothermal synthesis method. They investigated the potential of the WO2.72 nanowire bundles to be used as a cathode electrode for electrochromic devices and the effect of the Li+ insertion (or extraction) kinetics and diffusion of Li+. An electrode consisting of arrays of WO2.72 nanowire bundles was formed and used in an experiment using the Langmuir-Blodgett technique. The one-dimensional nanostructure of WO2.72 has a high Li-ion diffusion coefficient (similar to 5.2x10(-11) cm(2)/s) and low charge transfer resistance (similar to 28.6 Omega), which result in its having a fast electrochromic response time (coloring time < 3.5 s, bleaching time < 1.1 s), and outstanding high coloration efficiency (>55 cm(2)/C). (c) American Institute of Physics.