ARC Study of LiFePO4with Different Morphologies Prepared via Three Synthetic Routes

We report on the thermal stability of lithium iron phosphate (LiFePO4) cathode material as investigated by accelerating rate calorimetry (ARC). LiFePO4 (LFP) was prepared using three different synthetic methods, namely, solid state (P1), hydrothermal (P2) and molten state (P3) and have different particle sizes (in the range of ∼100 nm–3 μm) and different surface areas (in the range of ∼6–14 m2 g−1). The thermal stability was evaluated, prior and after charging LiFePO4, in the presence of either carbonate solvents (ethylene carbonate (EC): diethyl carbonate (DEC) (1:2 v/v)) or electrolyte (1 M LiPF6 in the same solvent). In the presence of the electrolyte, LiFePO4 is shown to be stable up to 280°C or 220°C for uncharged or charged cathode materials, respectively. The surface area of LiFePO4 is found to affect the initial self-heating rate (SHR) of the charged materials reaction with the electrolyte, while the presence of the LiPF6 salt reduces significantly the SHR of the combustion reaction of carbonates solvent initiated by the oxygen released from the cathodes; forming Fe2P2O7 at elevated temperatures.