Exploring the morphology of LiFePO4 modified by ethylene glycol: An integrated computational-experimental study

abstract

Nowadays much research efforts have been dedicated to enhancing the electrochemical performance of LiFePO4, particularly through the control of its morphology and particle size. This study has been designed to understand, at the atomic level, several surface properties of the olivine structure LiFePO4. Calculations are performed using density functional theory, employing the exchange-correlation functional PBE and ultra-soft pseudopotentials on all atoms. Within this framework, electrostatic potential maps, Bader charges, surface energy and surface energy shifts are investigated. From the calculated surface energies, the thermodynamic equilibrium shape of the LiFePO4 is provided through a Wulff construction. A comparison is presented between the commercial LiFePO4 morphology and the LiFePO4 homologue which has been modified with ethylene glycol (EG) as a process control agent. Regarding the surface-EG interaction, the equilibrium morphology shows the (111) and (101) facets as the most favored, leading to the suppression of the others. Compared to other facets, EG donated more charge to the (101) facet, approximately 0.12 e. The EG tends to polarize the (101) facet slightly, while the others remain neutral, as evidenced by the electrostatic potential maps and Bader charge distribution. All the possible morphologies obtained, considering a surface energy decrease of half for one or two facets, are illustrated using the Wulff construction. Herein, a detailed discussion of the changes in morphology is proposed, which is supported by X-ray diffraction and microscopy studies. The experimental findings confirmed that during the surface modification of LiFePO4, with EG, the nanoparticles generally exhibited a rounded-like morphology, though faceted ones were also detected. © 2025 Elsevier B.V.