Synthesis and characterization of porous maghemite as an anode for Li-ion batteries

The synthesis of porous maghemite via a simple glycerol-mediated solution method was successfully accomplished. Thermal analysis, X-ray diffraction and Mössbauer spectroscopy results disclosed the formation of maghemite. The morphological and structural features of maghemite were characterized by scanning electron microscopy, high-resolution transmission electron microscopy, and nitrogen adsorption-desorption. The powder showed Brunauer-Emmett-Teller surface area of 285 m² g^-1 with micro-, meso- and macropores. The anode body was doctor bladed using primary powder with a binder and a conductive agent. Galvanostatic charge-discharge cycling of the porous maghemite exhibited a specific reversible capacity of approximately 1180 mAh g^-1 at 100 mA g^-1 current density, which was two times higher than that of common nanomaghemite with average particle size of 19 nm. The cell showed stability even at the high current charge-discharge rates of 3000 mA g^-1 and more than 94% retention. After multiple high current cycling regimes, the cell recovered to nearly full reversible capacity of ~1120 mAh g^-1 at 100 mA g^-1. The reason for this remarkable performance of the present anode was thought to be dependent upon the role of pores in increasing the surface area and resistance against volume changes during lithium insertion/extraction.