Modelling of phase equilibria of LiFePO₄‐FePO₄ olivine join for cathode material

Abstract

A thermodynamic model for the FePO 4 -LiFePO 4 olivine join has been developed in order to provide support for the understanding of the charge transport behaviour within the cathode material during the battery operation. The Gibbs energy model for the olivine solution is based on the compound energy formalism with long-range-order and has been calibrated using the CALPHAD method, permitting the computation of phase equilibria by Gibbs energy minimization techniques. The model can simultaneously reproduce the reported eutectoid reaction, the 3 low-temperature miscibility gaps, the enthalpy of mixing, and the change of the voltage plateau with temperature during the delithiation process, in agreement with the available experimental data. The spinodal decomposition, which is possibly associated with fast charge transport within the cathode material, involves up to two sub-spinodal decompositions. Hence, the unique low-temperature miscibility gap of this system is considered as a blend of the two sub-miscibility gaps.

Electrode and Electrolyte Materials From Atomistic Simulations: Properties of LixFEPO4 Electrode and Zircon-Based Ionic Conductors

“…MPO 4 orthophosphates, with M cations being transition metals, rare-earth elements or actinides, are ceramic materials of interest in various research fields, including geochronology (Williams et al, 2007), geothermometry (Andrehs and Heinrich, 1998;Mogilevsky, 2007), energy storage (Iyer et al, 2006;Yamada et al, 2006;Dunn et al, 2015;Dong et al, 2017;Cerdas et al, 2018;Phan et al, 2019), and nuclear waste management (Ewing and Wang, 2002;Neumeier et al, 2017a;Schlenz et al, 2018), to name but a few. Most of the potential applications come from high durability (e.g., radiation damage resistance) of these materials (Neumeier et al, 2017a;Phan et al, 2019). There exist large varieties of phosphate-based ceramics of different crystalline structures (e.g., cheralite, apatites, olivine, kosnarite, see Iyer et al, 2006;Neumeier et al, 2017a;Phan et al, 2019).…”

“…Most of the potential applications come from high durability (e.g., radiation damage resistance) of these materials (Neumeier et al, 2017a;Phan et al, 2019). There exist large varieties of phosphate-based ceramics of different crystalline structures (e.g., cheralite, apatites, olivine, kosnarite, see Iyer et al, 2006;Neumeier et al, 2017a;Phan et al, 2019). The orthophosphates of interest for energy storage, FePO 4 and LiFePO 4 , have olivine-type structure of orthorombic space group symmetry of Pnma in which Fe exists in an octahedral environment (Iyer et al, 2006;Maxisch and Ceder, 2006, see Figure 1 for visualization of the structures).…”

“…LiFePO 4 materials are one of the best known candidates for energy storage electrodes (Dunn et al, 2015;Cerdas et al, 2018). These exhibit high theoretical energy density of 170 mAh/g and voltage of 3.5 V (Phan et al, 2019). Because of this, these materials are considered for large scale energy storage devices, including batteries for hybrid and electric automobiles (Prosini et al, 2002;Dunn et al, 2015;Cerdas et al, 2018).…”

“…Because of this, these materials are considered for large scale energy storage devices, including batteries for hybrid and electric automobiles (Prosini et al, 2002;Dunn et al, 2015;Cerdas et al, 2018). Intercalation of Li ions into FePO 4 results in formation of a solid solution between Li cations and vacant sites (Phan et al, 2019). Depending on the sizes of mixing species, a solid solution compounds could form a thermodynamically stable solid solution or a compound with a mixture of two phases, each rich in one of the cations Ji et al, 2019a).…”

“…Such a temperature-dependent maximum solubility offers opportunity to use such a system as geothermometer (Andrehs and Heinrich, 1998;Mogilevsky, 2007). It is known from experiment that Li x FePO 4 solid solution posses a wide miscibility gap at ambient temperature (Yamada et al, 2006;Meethong et al, 2007;Phan et al, 2019). In particular, studies of Yamada et al (2006) low Li solubility limits in Li x FePO 4 system at x = 0.05 and 0.89.…”