Ionothermal synthesis and electrochemical analysis of Fe doped LiMnPO4/C composites as cathode materials for lithium-ion batteries

• LiMn0.95Fe0.05PO4 particles prepared by ionothermal synthesis method are effective.
• The effect of the properties of [EMIM]OTf and [BMIM]OTf in ionothermal synthesis is studied.
• The obtained LiMn0.95Fe0.05PO4/C exhibit shuttle shape and favorable electrochemical properties.

Shuttle shaped and Fe doped LiMnPO4 particles are successfully synthesized via an ionothermal routine in 1-ethyl-3-methylimidazolium trifluoromethanesulfonate [EMIM]OTf and 1-buty-3-methylimidazolium trifluoromethanesulfonate [BMIM]OTf at 260 °C, respectively. And then, the carbon coated product of cathode materials can be efficiently prepared by a subsequent short calcination process. Scanning electron microscopy and field emission transmission electron microscopy shows that these as-prepared particles with the mean width of about 200 nm and length of 800 nm were coated by uniform carbon layers, which could improve the electronic conductivity of the final product effectively. The DLi values of samples that prepared in two ionic liquids above were calculated to be 1.36 × 10−13 and 4.61 × 10−14 cm2 s−1, respectively. It can be attributed to the LiMn0.95Fe0.05PO4/C particles prepared in [BMIM]OTf present more uniform distribution and smaller size. Thus, it deliver high discharge capacities of 159.2, 146.0, 135.1, 125.3, 115.5 and 84.4 mA h g−1 in the voltage range of 2.5–4.5 V at charge–discharge rate of 0.1, 0.2, 0.5, 1, 2 and 5 C, respectively.