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

Abstract

To improve the electrochemical performance of LiMnPO₄, a modified polyol reaction has been successfully developed for the preparation of LiMn_xFe_1−xPO₄/C samples (x = 0.2, 0.5, 0.8). The secondary particles of the acquired LiMn_xFe_1−xPO₄/C samples are spherical or annular, and the primary particles are nano-sized (20–80 nm). The LiMn_0.8Fe_0.2PO₄/C has a higher energy density of 637 W h kg⁻¹ compared with LiMn_0.2Fe_0.8PO₄/C (575 W h kg⁻¹) and LiMn_0.5Fe_0.5PO₄/C (584 W h kg⁻¹). The TEM image shows that the primary particles of LiMn_0.8Fe_0.2PO₄/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 LiMn_0.8Fe_0.2PO₄/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.