Controlled generation and tuning the oxygen defects in nanofibers of Ca2Fe2O5 toward high and stable Li-ion battery anode

In this work, we have attempted to create the oxygen defects in Ca 2 Fe 2 O 5 (C2FONF) nanofibers via electrospinning technique and subsequent heat-treatment on as-spun nanofibers such as 700 °C (C2FONF-700), 800 °C (C2FONF-800), and 900 °C (C2FONF-900). Further, it is observed that C2FONF-900 sample consists of larger particle size, smaller surface area and highest number of oxygen defects as comparison to other as-prepared samples. As an LIB anode, C2FONF-900 exhibits better cyclic performance and rate capability. Furthermore, highest capacitive Li + storage is observed in C2FONF-900 which significantly related to the higher presence of oxygen defect and, thus, provides better rate performance. • Generation and tuning the oxygen defects in Ca 2 Fe 2 O 5 (C2FONF) nanofibers via electrospinning technique. • All the as-prepared samples are thoroughly characterized by XRD, FE-SEM, BET, XPS and I-V. • The influence of particle size, surface area and oxygen defect on the Li-storage properties of all the C2FONF samples are studied. • The sample having highest number of oxygen defects among others exhibit better cyclic and rate performance. • The presence of higher oxygen defects leads to the larger contribution of capacitive Li + storage which further provide excellent rate capability in C2FONF. In recent years, oxygen-defect (vacancies) and nanostructured-based materials have been fabricated and applied as electrode materials for lithium-ion batteries (LIBs). However, the individual role of oxygen defects and nanostructuring on the improvement of Li-storage performance is still not clear. In addition, the technique which generates the control amount of oxygen-defects as well as maintains the nanostructured morphology of the electrode materials is highly desirable. Hence, in this work, we have attempted to create the oxygen defects in Ca 2 Fe 2 O 5 (C2FONF) nanofibers via electrospinning technique and subsequent heat-treatment on as-spun nanofibers such as 700 °C (C2FONF-700), 800 °C (C2FONF-800), and 900 °C (C2FONF-900). All the as-prepared samples are characterized by XRD, FE-SEM, BET, XPS, and I-V characteristics. From the quantification of oxygen defect, it is observed that C2FONF-900 sample consists of the highest number of oxygen defects. As an LIB anode, C2FONF-900 exhibits superior reversible capacity (530 (±10) mAh g −1 at 50 mAg −1 up to 100 cycles), cyclability (370 (±10) mAh g −1 at 1C: 500 mAg −1 up to 100 cycles). Further, the rate capability of C2FONF-900 is found better than the C2FONF-700 and C2FONF-800. Furthermore, the study of capacitive/diffusion-controlled process showed the higher contribution of capacitive capacity in the C2FONF-900 electrodes, which is responsible for their better rate capability. In this study, we have shown that the Li-storage properties of iron-based oxides can be easily improved by tuning their concentration of oxygen defects while maintaining similar fibric nanostructure.