Classical electrodes for Li-ion technology operate by either single-phase or two-phase Li insertion/de-insertion processes, with single-phase mechanisms presenting some intrinsic advantages with respect to various storage applications. We report the feasibility to drive the well-established two-phase room-temperature insertion process in LiFePO4 electrodes into a single-phase one by modifying the material's particle size and ion ordering. Electrodes made of LiFePO4 nanoparticles (40 nm) formed by a low-temperature precipitation process exhibit sloping voltage charge/discharge curves, characteristic of a single-phase behaviour. The presence of defects and cation vacancies, as deduced by chemical/physical analytical techniques, is crucial in accounting for our results. Whereas the interdependency of particle size, composition and structure complicate the theorists' attempts to model phase stability in nanoscale materials, it provides new opportunities for chemists and electrochemists because numerous electrode materials could exhibit a similar behaviour at the nanoscale once their syntheses have been correctly worked out.