Synthesis and characterization of LiMnPO₄/C nano-composites from manganese(ii) phosphate trihydrate precipitated from a micro-channel reactor approach

Compared with LiFePO₄, LiMnPO₄ offers 20% higher energy density, but suffers from several orders lower electronic and ionic conductivity. The strategy usually adopted to overcome these intrinsic drawbacks is particle nanosizing mainly achieved by wet chemical methods or solid-state reactions in molten hydrocarbon, but which are not suitable for scale-up. A novel, economic and scalable method is proposed, using a T type micro-channel reactor to continuously precipitate nano-Mn₃(PO₄) ₂·3H₂O for the first time. With the characterization of X-ray diffraction (XRD), transmission electron microscopy (TEM) and inductively coupled plasma (ICP), the generated Mn₃(PO ₄)₂·3H₂O is proved to have an orthorhombic structure, a lath shape and possesses very high purity. The optimized temperature to prepare LiMnPO₄/C nano-composites from the obtained Mn₃(PO₄)₂·3H₂O via a solid state reaction is proved to be 650 °C. The resulting sample is characterized by XRD, field emission scanning electron microscopy (FESEM), carbon/sulfur analysis, galvanostatic charge-discharge tests and alternating current impedance measurements. With 4.54 wt% of in situ carbon coating, this sample exhibits 137 mA h g^-1 at 0.05 C and relatively good capacity retention. Moreover, by minimizing the impurities, the LiMnPO₄ obtained from this novel method presents much improved Li⁺ diffusion coefficient due to less blocked [010] channels for Li⁺ migration.