Li_0.5Fe_2.5O₄ nanoparticles of about 80 nm were synthesized through a hydrothermal method, followed by a solid state reaction between LiOH·H₂O and Fe₂O₃. The Li_0.5Fe_2.5O₄ nanoparticles exhibit a remarkable high capacity (up to 1124 mA h g⁻¹), a good cycle stability (650 mA h g⁻¹ after 50 cycles) and excellent coulombic efficiency.