PNNL

Abstract

In this paper we report the influences of the initial lithium content on the structural, electrochemical and magnetic properties of nonstoichiometric LixMnPO4 (0.5=x=1.2) nano-particles. It has been revealed Mn2P2O7 is the main impurity when Li1.0. The different functions of Mn2P2O7 and Li3PO¬4 impurities in the non-stoichiometric compounds have been investigated systematically. At a slow rate of C/50 the reversible capacity of both Li0.5MnPO4 and Li0.8MnPO4 increases with cycling indicating a gradual activation of more sites to accommodate a reversible diffusion of Li+ ions which may be related to the interaction between Mn2P2O7 and LiMnPO4 nanoparticles. Among all the different compositions, Li1.1MnPO4 exhibits the most stable cycling ability probably due to the existence of a trace amount of Li3PO4 impurity which functions as a solid state electrolyte on the surface. The magnetic properties and X-ray absorption spectroscopy (XAS) of MnPO4?H2O precursor, pure and carbon coated LiMnPO4 and all the other non-stoichiometric LixMnPO4 are also investigated to identify the key steps to prepare a high performance LiMnPO4.