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

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.