Optimizing Carbon Coating Process for Lithium-Rich LiFePO4 Cathode Materials.

Abstract

Li1+xFe1-xPO4 (Li-rich LFP) has been proposed as an alternative to address low ionic and electronic conductivity of stoichiometric LiFePO4 (LFP). However, comprehensive studies investigating the impact of the carbon coating process on crystal structure and electrochemical performance during the synthesis of Li-rich LFP are still lacking. In particular, the characteristics of carbon precursor and calcination atmosphere significantly influence formation of crystal structure and electrochemical properties of the Li-rich LFP, underlining the necessity for further investigation. In this study, we compare two synthesis process: introducing carbon precursor before formation of LFP crystal structure (C/BLF) and adding it an additional calcination step after structure has formed (C/ALF). The C/ALF process sample has a larger unit cell volume and denser coating layer. As a result, the C/ALF sample exhibits a lower overpotential (0.54 V) and a higher discharge capacity (~134.13 mAhg-1) than C/BLF sample. These findings elucidate the influence of carbon coating process sequence on crystal structure and electrochemical performance during the synthesis of Li-rich LFP.