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Iron and vanadium oxides have a rich structural chemistry when combined with phosphate groups; the transition metal most commonly in an octahedral coordination. The inductive effect increases the potential difference between Fe3+/Fe2+ and Li/Li+ couples in phosphate lattices relative to the pure iron oxides; a similar behavior is found for the corresponding vanadium compounds. Of the iron phosphates, the olivine phase LiFePO4 has high thermal and chemical stability, even when lithium-free; the challenges of low electronic conductivity are being overcome, but data is lacking on the true lithium diffusion behavior. The all-ferric lipscombite-type phase, Fe1.33PO4OH, shows the highest capacity of the iron phosphates for lithium intercalation. The ε-VOPO4 material, formed by the oxidative de-intercalation of protons from H2VOPO4, can reversibly react with two lithium atoms in two steps. The face- and edge …