Single-Phase Lithiation and Delithiation of Simferite Compounds Li(Mg,Mn,Fe)PO₄

Abstract

Understanding the phase transformation behavior of electrode materials for lithium ion batteries is critical in determining the electrode kinetics and battery performance. Here, we demonstrate the lithiation/delithiation mechanism and electrochemical behavior of the simferite compound, LiMg_0.5Fe_0.3Mn_0.2PO₄. In contrast to the equilibrium two-phase nature of LiFePO₄, LiMg_0.5Fe_0.3Mn_0.2PO₄ undergoes a one-phase reaction mechanism as confirmed by ex situ X-ray diffraction at different states of delithiation and electrochemical measurements. The equilibrium voltage measurement by galvanostatic intermittent titration technique shows a continuous change in voltage at Mn³⁺/Mn²⁺ redox couple with addition of Mg²⁺ in LiMn_0.4Fe_0.6PO₄ olivine structure. There is, however, no significant change in the Fe³⁺/Fe²⁺ redox potential