The structural, electronic and Li diffusion properties of LiFeSO4F were analyzed by first-principles calculation under the DFT + U framework. The difference of the calculated lattice parameters and the reported data is within 3%. The redox potential of Fe2+/Fe3+ versus Li metal is 3.7 V. and phase separation of LiFeSO4F and FeSO4F is expected during Li extraction. Pure LiFeSO4F is an insulator with a band gap of 3.6 eV, while the band gap in the partially delithiated form Li1-xFeSO4F is obviously smaller. A very low Li migration energy of 0.3 eV is required in the partially delithiated form Li1-xFeSO4F, and the diffusion coefficient is estimated to be about 1.6*10(-7)cm(2)s(-1). (C) 2010 Elsevier B.V. All rights reserved.