Utilizing active multiple dopants (Co and Ni) in olivine LiMnPO4

Parent LiMnPO4 and variants with cobalt and nickel on Mn (M2) site in LiMnPO4 olivine are synthesized by sucrose induced combustion method. The synthesized cathodes are tested in aqueous based LiOH electrolyte. The observed change in lattice parameters and peak positions for the olivine variants evidenced that doping occurred in the lattice without any disruption. The nickel and cobalt variants in the LiMnPO4 olivine mitigated the lattice distorted Jahn-Teller Mn3+ ions, thus the electrochemical performance was enhanced with a discharge capacity of 94 mA h/g. The doped LiMn0.5Co0.5PO4 and LiMn0.33Co0.33Ni0.33PO4 cathodes showed a smaller particle size having a lower Li+ or electron transport length. Influence of high voltage Co and Ni-based dopants compared to the low voltage Mn-based LiMnPO4 showed a superior redox potential and was able to access Co3+/Co2+ and Ni3+/Ni2+ in a safe operating voltage window which is plausible for aqueous electrolytes. Whereas LiCoPO4 and LiNiPO4 are difficult to assess in non-aqueous electrolytes, this is due to the electrolyte instability at the high operating voltage. Improved cell voltage with extended cell capacity and good capacity retention for mixed dopants in olivine is reported.

► The role of fuel played a role in controlling the morphology of the combustion derived olivine.
► Replacing part of Mn atoms in LiMnPO4 by Ni and Co mitigated the Jahn-Teller Mn3+ ions.
► Cyclic voltammetry showed multiple dopants Co and Ni in Mn sites are energetically favorable.
► Multiple dopants increased the discharge capacity and capacity retention.