Low Temperature Aqueous Precipitation Synthesis of LiMnPO4 Nano Particles for Li Ion Battery Cathodes

Abstract

LiMnPO4 (LMP) is regarded as a promising material for improved Li ion batteries. It is, like the already commercially applied LiFePO4 (LFP), an olivine cathode material. The main advantage is its higher potential (4.1V vs. 3.5V for LFP, with respect to Li+/Li), resulting in an energy density, about 20% higher than for LFP. The main drawbacks are its low electronic and ionic conductivities (compared to LFP). This results in reduced experimental capacities, especially at elevated (dis)charging rates1. This drawback can be circumvented, by reducing particle sizes to nano dimensions, resulting in shorter Li ion diffusion distances. Here, we describe an optimized LMP low temperature (100°C) aqueous precipitation synthesis method2, resulting in nanoparticles (NP), with typical sizes of 50-200 nm, of which the reaction time could be significantly reduced, by modifying the base, used for inducing the precipitation. By an in-depth study of several synthesis parameters such as the flow rate, reaction time, temperature, base, … the complexity of this thermodynamically and even kinetically fragile system is emphasized. Our results show that phase pure LMP NP are only obtained in a particular small subset of these parameter values. Outside this range, secondary phases (like Li3PO4, MnHPO4 hydrate and Mn5(HPO4)2(PO4)2.4H2O (hureaulite)) are formed, or LMP is even completely absent. The figure shows a TEM image of the LMP NP as synthesized after 24 hours at 100°C. T. Vranken is a Ph.D. fellow of the Research Foundation – Flanders (FWO). References (1) Wang, H.; Yang, Y.; Liang, Y.; Cui, L.-F.; Casalongue, H. S.; Li, Y.; Hong, G.; Cui, Y.; Dai, H. Angew. Chemie Int. Ed. 2011, 50, 7364–7368. (2) Delacourt, C.; Poizot, P.; Morcrette, M.; Tarascon, J.-M.; Masquelier, C. Chem. Mater. 2004, 16, 93–99.