Experimental and thermodynamic study of Li‐O and Li₂O‐P₂O₅ systems

Abstract

LiFePO 4 (LFP) as a promising cathode material has been extensively studied. However, the high cost of current batch production technology limits its application, especially in automotive industries. To develop the new melting synthesis of LFP, the process conditions have to be strictly controlled, such as temperature, composition, and the partial pressure of oxygen. Reliable and accurate thermodynamic information about Li-Fe-P-O systems could serve as a useful guide for designing operating conditions. As part of ongoing efforts, the Li-O and Li 2 O-P 2 O 5 binary systems have been first studied following the CALPHAD method using FactSage thermodynamic software. The data on thermodynamic properties (C p , enthalpy of formation, and vapour pressure) and phase diagrams (liquidus/solidus temperature, phase transition, and solid solubility) available in the literature were carefully reviewed and evaluated for the above-mentioned systems. The modified quasichemical model (MQM) with quadruplet approximation was used for the liquid phase in the present studies. This model simultaneously takes into account the short-range ordering of firstnearest-neighbours (FNN) and second-nearest-neighbours (SNN), which improves the thermodynamic description of the Gibbs energy of the liquid. The thermodynamic model parameters of the Gibbs energy have been obtained for all of the phases considered in the Li-O and Li 2 O-P 2 O 5 binary systems. DSC-TGA experiments on the selected four compositions were carried out to validate the liquidus and phase transition temperature reported in the literature. Overall, the self-consistent thermodynamic description using the model parameters obtained in this work can successfully reproduce the evaluated experimental data.

Fe3+ reduction during melt‐synthesis of LiFePO4

“…An examination of the thermodynamics of the Fe‐Fe 2 O 3 ‐LiPO 3 and Fe‐LiPO 3 systems, performed using FACTSage 7.0 and the model developed by Jin et al, shows that a eutectic forms along the Fe‐LiPO 3 rich axis at 1044 °C and 0.343 mol/mol of LiPO 3 (Figures ). This eutectic is consistent with the Fe‐P eutectic reported at 1048 °C, and the eutectic temperature could be lowered by the presence of carbon, as low as 952 °C for the Fe‐P‐C system .…”

Piloting melt synthesis and manufacturing processes to produce c‐lifepo4: preface

“…Jin et al applied the modified quasichemical model with sub‐lattices I and II, , to characterize the liquid phase. The model accounts for first‐nearest neighbours and second‐nearest neighbours.…”