Enhanced Performance of Sodium-Ion Battery Cathodes with Ti and V Co-Doped P2-Type Na0.67Fe0.5Mn0.5O2 Materials

Manganese- and iron-rich P2-type Na0.67Fe0.5Mn0.5O2 (NFM) has garnered significant interest as a promising cathode candidate due to the natural abundance of Fe and Mn along with a 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. In this research, a novel P2-type transition metal-oxide cathode Na0.67Fe0.5−2xMn0.5TixVxO2 was synthesized by doping a tiny fraction of two electrochemically inactive elements, Titanium (Ti) and Vanadium (V), into Mn-rich Na0.67Fe0.5Mn0.5O2 (NFM) that mitigated the JT effect substantially and ameliorated the stability of the SIB during cycling. These exhaustive structural and morphological comparisons provided insights into the effects of V and Ti doping on stabilizing surface structures, reducing Jahn Teller distortion, enhancing stability and capacity retention, and promoting the Na+ carrier transport mechanism. Moreover, the electrochemical analysis, such as the galvanostatic charge/discharge profile, validates the capacity improvement via Ti and V co-doping into NFM cathode. The initial discharge capacity of the 2% Ti/V-doped Na0.67Fe0.48Mn0.5Ti0.01V0.01O2 (2NFMTV) was found to be 187.12 mAh g−1 at a rate of 0.1 C, which was greater than the discharge capacity of 175.15 mAh g−1 observed for pure NFM (Na0.67Mn0.5Fe0.5O2). In contrast, 2NFMTV exhibited a noteworthy capacity retention of 46.1% when evaluated for its original capacity after undergoing 150 cycles at a rate of 0.1 C. This research also established a structural doping approach as a feasible technique for advancing the progress of next-generation Sodium-ion Batteries.