Synthesis and Characterization of Vanadium-Doped LiMnPO₄‑Compounds: LiMn(PO₄)_x(VO₄)_1–x (0.8 ≤ x ≤ 1.0)

In this paper we report on the increase of grain conductivity in the potential cathode material LiMnPO₄ by means of vanadium doping by 1–2 orders of magnitude. We found that up to 20% of phosphorus in LiMnPO₄ can be replaced by vanadium. The allocation of vanadium was investigated by a Rietveld analysis of high quality laboratory X-ray diffraction (XRD) data and Extended X-ray Absorption Fine Structure (EXAFS)/X-ray Absorption Near Edge Structure (XANES) measurements of the samples. Calculations of the electronic structure by means of density functional theory (DFT) help to understand an observed increase in conductivity, which is likely to be of electronic nature. We suggest that it is attributed to energetically low lying d-levels of vanadium, which above 0 K cause a partial formation of mixed-valence Mn²⁺/Mn³⁺.