Revealing the Effect of Oxygen Defects and Morphology on Li-Storage Performance of Calcium Iron Oxide

Abstract

Nanostructure design and modulation of ion/electron paths are effective strategies for achieving high-performance iron-based anode materials for next-generation Li-ion batteries (LIBs). In the present work, we attempt to explore the correlation among morphologies, defect concentration, transport phenomenon, and Li-storage performance of CaFe2O4 (CFO). Herein, two different morphologies (nanoparticles/nanofibers) of CFO are prepared by facile and cost-effective techniques and characterized by field emission scanning electron microscope (FE-SEM), thermogravimetric (TG), high-resolution transmission electron microscope (HR-TEM), and X-ray diffractometer (XRD). X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR) analysis revealed the presence of a higher concentration of oxygen defects in nanofibers of CFO, which further improves their conductivity and ionic transference number. As an anode for LIBs, the nanofibers of CFO exhibit excellent lithium storage performance with a reversible and stable capacity of 610 (±10) mAh g−1 (almost two times of their nanoparticles) and good rate capability. The improved Li-storage performance is attributed to morphological featured of nanofibric network as well as the presence of oxygen defects. Furthermore, The CFO nanofibers//self-prepared LiCoO2 full cell delivers a high energy density of 150 Wh Kg−1 (as per the total active mass of anode and cathode). Based on the cyclic voltammogram, galvanostatic charge/discharge cycling, ex situ - HR-TEM, XPS, and magnetic (M-H) studies, a possible Li-storage mechanism is also proposed.