The Mechanism of Capacity Enhancement in LiFePO4 Cathodes Through Polyetheramine Coating

This paper addresses the possible mechanisms underlying the capacity enhancement through polyetheramine [PEA, glyceryl poly(oxypropylene)triamine] coating on LiFePO4 (Phostech Lithium) particle surface. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared studies have confirmed the presence of PEA on the surface by the appearance of the N 1s peak in the XPS spectra and bands in the 2850-2960 cm(-1) wavenumber range of the IR spectra. Potentiostatic measurements in organic electrolytes have shown that the discharge capacity is increased ca. 12% compared to the as-received material, i.e., more Fe2+/Fe3+ ions are utilized during the redox process. This is due to better wettability of the electrolyte to the particle surface, which is indicated by the slower sedimentation of coated particles. Furthermore, cyclic voltammetry has shown that PEA-coated particles display higher capacity than the as-received material also in an aqueous electrolyte, which to some extent can be explained by the difference in wettability between the materials, but also by the protection of LiFePO4 from spontaneous formation of a Li3PO4 surface layer and Fe3+-containing solids when in contact with water.