Tannic Acid-Derived Carbon Coating on LiFePO4 Nanocrystals Enables High-Rate Cathode Materials for Lithium-Ion Batteries

Tannic acid (TA) is a plant polyphenol capable of coating hydrothermally grown LiFePO4 nanocrystals by simple wet impregnation and drying. Mild pyrolysis in an inert atmosphere transforms the TA coating on LiFePO4 nanocrystals into homogeneous and compact carbon films. Introducing conductive carbon films on LiFePO4 nanocrystals increases the electrical conductivity of the LiFePO4/C composite. However, reaction kinetics revealed that excessively thick carbon films limit the Li+ diffusivity of the LiFePO4/C composite during delithiation/lithiation. Therefore, the electrical conductivity and Li+ diffusivity must be balanced to achieve the required electrochemical properties.