The chemical, physical and electrochemical effects of carbon sources on the nano-scale LiFePO4 cathode surface

LiFePO4-C composite cathode active materials were synthesized by a sol-gel-assisted carbothermal reduction method using tannic (TA), tartaric (TRA) and stearic (SA) acids as both the carbon coating and reducing agent. The effect of different carbon sources on the structural, morphological and electrochemical properties of LiFePO4 are studied in this paper. The samples were characterized by optical-analytical methods and galvanostatic charge discharge tests. The scanning electron microscopy (SEM) images revealed that the majority of the particles lay between 300 and 500 am for pure LiFePO4, while the carbon-coated LiFePO4 particles were from 50 to 300 nm. Furthermore, we found that TA is suitable for producing a LiFePO4-C composite with a fine particle size and a uniformly-coated carbon conductive layer (3.6 nm thickness) by high resolution transmission electron microscopy (HR-TEM). The cycling studies indicated a high and stable discharge capacity of 151 mAh g(-1) for the carbon-coated nanocrystalline LiFePO4 with TA at room temperature. The current rate capability studies between 0.2-10 C (1 C=170 mAh g(-1)) demonstrated an excellent capacity retention efficiency of over 96.9% after 300 cycles. A schematic illustration was proposed based on the physical and chemical adhesion behaviors on the LiFePO4 surface of the three organic structures used as the carbon source. (C) 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved.