Modification of the LiFePO₄(010) Surface Due to Exposure to Atmospheric Gases

First-principles thermodynamics enables the description of the surface chemistry of inorganic materials as a function of temperature and partial pressures of atmospheric gases, providing a framework to connect atomistic simulations with macroscopic materials properties. Here we re-examine the surface chemistry of LiFePO4 (LFP), a widely studied material for use as the cathode in Li-ion batteries. Our results reveal that at room temperature and under standard pressures the LFP (010) surface is covered with water. At elevated temperatures and reduced H2 partial pressure, one water molecule loses a hydrogen atom and the preferred binding moieties are OH and H2O; while further reducing the H2O partial pressure results in the desorption of water leaving only the OH behind. This work also shines new light on the configuration, and resulting electronic properties, of the LFP (010) surface when molecular oxygen (O2) is adsorbed. The molecular adsorbates are also shown to have an impact on the LFP surface potentials and magnetic properties. These simulations provide an enhanced picture of the LFP surface chemistry and the potential impact of these adsorbates on understanding the characteristics of LFP in different materials applications.