Effects of organic phosphorus acid on the core-shell structure and electrochemical properties of LiFePO4 uniformly wrapped with in-situ growed graphene nanosheets

Organic acid, ethylenebis(nitrilodimethylene) tetraphosphonic acid (EDTMPA), is a kind of eco-friendly phosphorous acid with special chelation and reducing function groups. It has been applied to fabricate LiFePO4@Graphene (LFP@G) nanocomposites. The microstructure and electrochemical properties of the LFP@G have been investigated by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Raman spectroscopy and electrochemical testing techniques. The results indicate that the graphene is in the form of nano-sized sheets which in-situ growed and wrapped around LiFePO4 particles to form a unique core-shell structure. The formation of the core-shell structure is owing to the special chelation and reducing functional groups in the EDTMPA molecules. It is also found that the fabricated LiFePO4@Graphene has a particle size of below 100 nm with high purity. Further on, the fabricated LFP@G exhibits a high reversible capacity of 161.8 mAh g (1) at 0.2 C rate, and an excellent rate capacity of 125.9 mAh g (1) at 10 C, which shows a great potential as a superior cathode material for lithium-ion batteries. The present work also elucidates the mechanism of how the special core-shell structure LiFePO4@Graphene can benefit the Li+ migration during the charge/discharge processes and improve the electronic conductivity of the LFP@G nanocomposites. (C) 2017 Published by Elsevier B.V.