Evaluation of real performance of LiFePO4 by using single particle technique

Abstract

Single particle technique was employed to investigate the intrinsic electrochemical properties of LiFePO4. A micro-size LiFePO4 single particle composed of a plurality of primary particles was contacted with a micro Pt electrode in an electrolyte solution using a micromanipulator under optical microscope observation, and then galvanostatic charge/discharge tests were performed. The specific capacity of the particle with a diameter of 24μm was estimated to be 1.5nAh in the potential rage of 2.0–4.2V vs. Li/Li+. The particle had a good reversibility for charge/discharge processes, and also showed excellent rate performance, for example, that more than 50% of the full capacity was maintained even when the discharge current was as high as 750nA corresponding to 4s discharge (900C rate). From the dependency of over-potential in the single particle electrode on discharge current density, it was expected that the discharge reaction was controlled at the discharge current densities higher than 2.56mAcm−2 by Li+ diffusion step in the particle accompanied with the phase conversion from FePO4 to LiFePO4. According to this assumption, Li+ diffusion coefficient in the particle was estimated as 2.7×10−9cm2s−1.