Preparation and electrochemical properties of Li3V1.8Mn0.2(PO4)3 doped via different Mn sources

This work attempts to substitute V of Li3V2(PO4)3 (LVP) by the doped ion of manganese with the valence of +2, +3 and +4 and various ionic radiuses. A series of Mn-doped LVP composites (LVMP) by different manganese sources are synthesized by sol-gel and heat-treatment. Manganese ion with the valences of +3 and +4 have been successfully inserted into the lattice of Li3V2(PO4)3 to form a stable solid-solution even the substitution mole ratio reaches to 0.2, except the impurity phase of LiMnPO4 in LVMP when manganese ions with the valence of +2 involve in the substitution. Mn2+ exists in all three samples as expected, but the main valence state of Mn ions in LVMP-A, LVMP-B and LVMP-C are Mn4+, Mn3+ and Mn2+, respectively. LVMP-B (MnOOH as dopant) delivers the highest capacity of 137 mAh g−1, than LVMP-A (MnO2 as dopant) 125 mAh g−1 and LVMP-C (Mn3O4 as dopant) 123 mAh g−1. LVMP-B shows the best cycle performance, remaining 98% of the initial capacity after 50 cycles in range 3.0-4.3 V. Mn source of MnOOH properly substituted the structure of LVP enhances the lithium diffusion ability and stability of LVP during charge/discharge.