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Effects of Fe2+ ion doping on LiMnPO4 nanomaterial for lithium ion batteries

To improve the electrochemical performance of LiMnPO4, a modified polyol reaction has been successfully developed for the preparation of LiMnxFe1−xPO4/C samples (x = 0.2, 0.5, 0.8). The secondary particles of the acquired LiMnxFe1−xPO4/C samples are spherical or annular, and the primary particles are nano-sized (20–80 nm). The LiMn0.8Fe0.2PO4/C has a higher energy density of 637 W h kg−1 compared with LiMn0.2Fe0.8PO4/C (575 W h kg−1) and LiMn0.5Fe0.5PO4/C (584 W h kg−1). The TEM image shows that the primary particles of LiMn0.8Fe0.2PO4/C are uniformly covered by a 3 nm carbon layer, and it can deliver a high discharge capacity of 161 mA h g−1 at 0.05C. At a 0.5C discharge rate, the LiMn0.8Fe0.2PO4/C can maintain 80.4% of its initial capacity after 900 cycles, and it also maintains 90% and 83% of its initial capacity at 45 °C and 55 °C respectively after 100 cycles. The results demonstrate that the modified polyol process is feasible for Fe-doping and carbon-coating to enhance the electrochemical performance of LiMnPO4.