Role of Oxygen Deficiency and Microstructural Voids/Gaps in Nanostructures of Ca2Fe2O5 as an Anode Toward Next-Generation High-Performance Li-Ion Batteries

Recently, naturally abundant, low-cost, and high-capacity iron-based metal oxides have attracted much attention as anodes for next-generation Li-ion batteries. However, their practical applications have been impeded by low electronic/ionic conductivity and a poor cycle life resultant of their drastic volume expansion/shrinkage during cycling. Herein, two nanostructures (nanoparticles and nanofibers) of Ca2Fe2O5 (C2FO) are fabricated and well characterized by FE-SEM, TGA, XRD, XPS, HR-TEM, and EPR. Nanofibers of C2FO exhibit almost two-times higher capacity than the presently employed commercial graphite. Further, excellent cyclability (up to 250 cycles) and rate capability are demonstrated by C2FO nanofibers. On the other hand, nanoparticles of C2FO are found to be inferior to the nanofibers of C2FO. XPS and EPR techniques reveal a greater presence of oxygen vacancies in the C2FO nanofibers, which improve the electronic/ ionic conductivity of C2FO. In this study, we have shown that it is not only a good matrix element such as CaO but also a unique morphology as well as a high concentration of oxygen vacancies that is essential to get a high and stable capacity in cheap, green, and abundant Fe-based electrode materials. Furthermore, the viability of Ca2Fe2O5 nanofibers is also tested in full cell configuration with a LiCoO2 cathode.