Morphology and Oxygen Defects Mediated Improved Pseudocapacitive Li+ Storage of Conversion-Based Lithium Iron Oxide

Conversion-based oxides, particularly iron oxides, are projected to be viable, green, and cost-effective materials for Li-ion battery (LIB) anode. However, their low electronic/ionic conductivity, inferior initial coulombic efficiency (ICE), and poor cyclic/rate performance are some of the challenges. To address these issues, a combined approach of utilizing the nanostructures of iron oxides and creating oxygen defects in them may be an effective strategy to improve their Li-storage performance. Thus, in the present work, nanostructures (nanoparticles/nanofibers) of lithium iron oxides (LiFe5O8, LFO) are prepared and thoroughly characterized by FE-SEM, TEM, TG, XRD, BET, and i-v characteristics. XPS and EPR analyses are carried out to quantify the oxygen defects in the as-prepared samples. LFO nanofibers shows better conductivity (almost 5.5 times higher) than their corresponding nanoparticles, which was ascribed to the presence of a higher concentration of oxygen defects in the nanofibers. Further, as LIB anode, nanofibers of LFO exhibits a two times greater specific capacity, i.e., 505 (+/- 10) mAh g(-1) at 50 mA g(-1), after 60 cycles and higher pseudocapacitive Li+ storage. Further, a better rate performance of LFO nanofibers is observed as compared to LFO nanoparticles. Moreover, ex-situ measurements (XRD, XPS, and M-H) were also carried out to identify the Li-storage mechanism during the lithiation/delithiation process. Furthermore, the practical application of LFO nanofibers as LIB anode was tested in a full cell configuration and delivers an energy density of 160 (+/- 5) Wh kg(-1) (according to the total active mass of the anode and cathode). In this study, we have shown that how one can tune the Li kinetics oxygen defects/morphology and thereby the Li-storage properties of cost-effective and green iron-based material.

Automated summary

Iron oxides, particularly in nanostructured form with oxygen defects, show improved Li-storage performance for Li-ion battery anodes. Nanofibers of lithium iron oxides exhibit higher conductivity and specific capacity compared to nanoparticles, along with better rate performance and pseudocapacitive Li+ storage. Ex-situ measurements confirm the improved Li-storage mechanism and practical energy density of the nanostructured iron-based material for LIB anodes.