Synthesis and Characterization of the LiMnP_1–xV_xO_4–δ Solid Solutions

Abstract

Compounds with the olivine-type structures are considered as perspective materials for lithium-ion power sources for both industrial and transport applications. Lithium iron phosphate is most highly developed from this family, but LiMnPO4 is supposed as much promising, due to its higher EMF vs. lithium. One of the main lacks of this class of materials is the low electronic conductivity. The traditional ways of conductivity increase by partial replacement of Mn with other transition metal for LiMnPO4 do not result to essential success. Our approach consisting in the influence onto anion sublattice results to better effect. Such solid solutions should be suitable for oxygen nonstoichiometry creation in virtue of ability of vanadium ion for oxidation degree downturn. Using magnetic methods, we succeeded to show that the required solid solutions are really formed. The optimal synthesis conditions of LiMnP1-xVxO4-δ solid solutions were determined. It was shown, that the doping of LiMnPO4 by vanadium jointly with oxygen nonstoichiometry brings to substantial enhance of electronic conductivity in this material. Observed peculiarities of the magnetic properties indicate the restructuring in the local environment in anion sublattice.

Effect of vanadium doping on the magnetic properties of LiMnPO4

“…The allocation of vanadium in LiMnPO 4 was investigated using a number of diffraction and spectral methods , which like the results of the ab initio calculations , clearly indicated that the vanadium atoms in the vanadium‐substituted LiMnPO 4 indeed occupy the phosphorus sites. Vanadium is an element with variable valence.…”

“…The similarity between the electronic structures of pentavalent vanadium and phosphorus makes it possible to substitute V for P in PO 4 groups in a wide range. What does matter is that vanadium improves the electrochemical properties of LiMnPO 4 presumably owing to the increase in electronic conductivity .…”

Some aspects of antiferromagnetic ordering in LiMnP0.85V0.15O4: Neutron diffraction and DC-magnetization studies

“…According to [36], vanadium doping can improve the electrochemical properties of LiMnPO 4 presumably owing to the increase of electronic conductivity. The positive effect of vanadium on the electrochemical properties of lithium metal phosphate described for vanadium-modified LiCoPO 4 too [37].…”

“…Appropriate amounts of reagents were mixed and milled to the average particle size less than 1 mm. The sample was compacted and thermally treated twice under pure argon flow for 6 h at temperature 820 1C [36].…”

Synthesis and Characterization of Vanadium-Doped LiMnPO4-Compounds: LiMn(PO4)x(VO4)1–x (0.8 ≤ x ≤ 1.0)

“…There are only few reports on LiMnPO 4 compared to the number on LiFePO 4 . Most studies on LiMnPO 4 have concentrated on decreasing the sizes of the grains forming the material and thereby reducing the transport distances for different charge carriers. − ,− Moreover, except for some studies on solid solutions of the type LiMn 1– y Fe y PO 4 , only little work has examined other doping attempts for LiMnPO 4 . , Attempts for replacing the phosphorus by other elements have only been reported by Kellerman et al who tried to incorporate vanadium on that position (for a more detailed discussion of their results, see below).…”