Extenuation of Jahn-Teller Distortion By Ti and V Co-Doping in P2 Type Sodium Iron Manganese Oxide Cathode

Abstract

Among all the prevailing cathode materials for Sodium-Ion Battery (SIB), the Manganese and Iron rich P2 type Na2/3Fe1/2Mn1/2O2 (NFM) has attracted broad attention as a promising cathode candidate due to the natural abundancy of Fe and Mn along with high redox couple of Fe3+/Fe4+ and Mn3+/ Mn4+. Despite all these merits, NFM suffers from structural instability during cycling arising from the destructive Jahn-Teller (JT) distortion effect of Mn3+/ Mn4+ during charging and Fe4+/ Fe3+ during discharging. This study investigates how the elemental doping process effectively alleviates the JT effect. Here, in this research, a tiny fraction two electrochemically inactive elements, Titanium (Ti) and Vanadium (V) are incorporated in Mn-rich cathode that mitigated the JT effect substantially and ameliorated the stability of the SIB during cycling. A moderate amount of doping preserves the lattice structure and similar morphology to pristine NFM which is attested from FESEM and EDS mapping results. Besides, the Ti and V co-doping in place of Fe not only effectively reduced the amount of JT prone Mn3+, which is observed through in-depth material analysis such as XRD and XPS, but also increased the specific capacity by expanding the d-spacing for Na ion transport that are reflected through various electrochemical analysis.