Effect of manganese doping on conduction in olivine LiFePO4

Abstract

Lithium ion batteries play a crucial role in terms of good rechargeability, long cycles and higher shelf life. For the fabrication of such a Li ion battery, properties of cathode material can be engineered keeping anode and electrolyte fixed. In the present work, lithium iron phosphate (LiFePO4) has been utilized as cathode material and the properties of LiFePO4 have been tuned by doping manganese (Mn). LiFePO4 and different concentrations of Mn doped LiFePO4 were prepared by solid state route. X-Ray diffraction and Raman studies were performed to confirm the formation of LiFePO4 and Mn doped LiFePO4 in olivine structure. Cyclic voltammetry studies revealed maximum peak oxidation current (2.96 mA) and largest surface coverage (0.066 nanoMoles/cm2) for the LiFePO4 doped with 15% Mn (LiMn0.15Fe0.85PO4). AC-conductivity study was carried out for different frequencies at room temperature. The conductivity parameters estimated using Almond and West formalism support the cyclic voltammetry results. Ion-hopping rate (ω p ) and charge carrier concentration (K) maximize for 15% Mn doping (ω p : 582974.48719 Hz; K: 2.62447 × 10−6) and drop on either increasing (ω p : 167134.73521 Hz; K: 1.25647 × 10−7) or decreasing (ω p : 130726.49084 Hz; K: 2.52435 × 10−6) the Mn doping. The increase till 15% Mn doping has been attributed to the increase in unit cell volume with Mn doping while the sudden decrease at 20% Mn doping is due to dominance of back-hopping mechanism. The results clearly indicate that 15% Mn doped LiFePO4 is the most appropriate for the realization of a cathode for Li-ion battery.