We present a first-principles electronic band structure for pure LiFePO4,{\mathrm{LiFePO}}_{4}, delithiated FePO4,{\mathrm{FePO}}_{4}, and Cr-doped LiFePO4.{\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 Fe2+{\mathrm{Fe}}^{2+} to Fe3+,{\mathrm{Fe}}^{3+}, but in agreement with the present x-ray photoemission spectroscopy experiment. Calculation also assumes a significant enhancement of electronic conductivity when lithium ions are replaced by cations with higher valence, Cr3+.{\mathrm{Cr}}^{3+}. We also confirm experimentally, for Li1\ensuremath−3xCrxFePO4{\mathrm{Li}}_{1\ensuremath{-}3x}{\mathrm{Cr}}_{x}{\mathrm{FePO}}_{4} with x=0.01x=0.01 and 0.03, an enhancement of the electronic conductivity up to eight orders of magnitude comparing with pure LiFePO4.{\mathrm{LiFePO}}_{4}. Besides the conventional p-type doping conductivity, another mechanism has been suggested, which involves the electron hopping within a cluster surrounding the doping atom and related vacancies, and electron tunneling between these conducting clusters.