Enhancement of electronic conductivity ofLiFePO4by Cr doping and its identification by first-principles calculations

We present a first-principles electronic band structure for pure ${\mathrm{LiFePO}}_{4},$ delithiated ${\mathrm{FePO}}_{4},$ and Cr-doped ${\mathrm{LiFePO}}_{4}.$ It indicates that not only Fe but also O atoms are oxidized in the delithiation process, while P is little affected. This is in contrast to the usual view of the intercalation reaction that the removal of Li only transforms Fe from ${\mathrm{Fe}}^{2+}$ to ${\mathrm{Fe}}^{3+},$ but in agreement with the present x-ray photoemission spect