Combined First-Principle Calculations and Experimental Study on Multi-Component Olivine Cathode for Lithium Rechargeable Batteries

The electrochemical properties and phase stability of the multi-component olivine compound LiMn(1/3)Fe(1/3)Co(1/3)PO(4) are studied experimentally and with first-principles calculation. The formation of a solid solution between LiMnPO(4), LiFePO(4), and LiCoPO(4) at this composition is confirmed by XRD patterns and the calculated energy. The experimental and first-principle results indicate that there are three distinct regions in the electrochemical profile at quasi-open-circuit circuit potentials of similar to 3.5V, similar to 4.1V, and similar to 4.7V, which are attributed 50 Fe(3+)/Fe(2+,) , Mn(3+)/Mn(2+), and Co(3+)/Co(2+) redox couples, respectively. However, exceptionally large polarization is observed only for the region near 4.1V of Mn(3+)/Mn(2+) redox couples, implying; an intrinsic charge transfer problem. An ex situ XRD study reveals that the reversible one-phase reaction of Li extraction/insertion mechanism prevails, unexpectedly, for all lithium compositions of Li(x)Mn(1/3)Fe(1/3)Co(1/3)PO(4) (0 <= x <= 1) at room temperature. This is the first demonstration that the well-ordered non-nanocrystalline (less than 1% Li-M disorder and a few hundred nanometer size particle) olivine electrode can be operated solely in a one-phase mode.