Effect of manganese doping on conduction in olivine LiFePO₄

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 (LiMn_0.15Fe_0.85PO₄). 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.