Enhanced electrochemical properties of LiFe1-xMnxPO4/C composites synthesized from FePO4•2H2O nanocrystallites

The high discharge potential of LiMnPO4, 4.1 V vs. Li/Li+, and its theoretical capacity of 170 mAh g(-1) make it a promising candidate as a cathode material in lithium-ion batteries. But extremely low electronics conductivity, slow lithium diffusion kinetics, and the Jahn-Teller effect of Mn3+ limit the electrochemical performances of LiMnPO4. In this work, the pre-synthesized and defined FePO4 center dot 2H(2)O nanocrystallites are used as one of the raw materials to synthesize LiFe1-xMnxPO4/C (x = 0.85, 0.75, 0.65) composites via solid-state reactions. The synthesized LiFe1-xMnxPO4 samples show well-crystallized structures and have enhanced electrochemical properties. There exist two plateaus around 3.5 and 4.1 V on both of their charge and discharge curves. Among the samples, the Fe0.25Mn0.75PO4 one exhibits the longest high-voltage charge/discharge plateau at 4.10 V/4.05 V, and has an average discharge voltage of similar to 3.78 V vs. Li/Li+ and a discharge capacity of similar to 130 mAh g(-1) at 0.05 C rate. For the Fe0.25Mn0.75PO4 sample, the noticeable improvement of its electrochemical performances is mainly attributed to iron substitution, the appropriate Mn/Fe ratio, and the well-ordered crystal structure forming by using FePO4 center dot 2H(2)O nanocrystallites as one of the raw materials. (C) 2012 Elsevier B.V. All rights reserved.