The extensive studies over the last decade have established Na-ion batteries (NIBs) as one of the cheaperalternatives to Li-ion batteries. P2-type Na0.67Ni0.33Mn0.67O2 has stood out among layered oxidebased electrode materials providing the best over-all electrochemical performance. The electrodes can exertup to 92.5% of its theoretical capacity (160 mAhg-1) at a voltage higher than 3 V accounted for the Ni2+/Ni4+redox. However, at higher voltages, electrodes suffer irreversibility due to P2-O2 structural transition.Recent studies in suppressing this transition by partial substitution with various metals on either Ni or Mnlattice site have suggested enhancing cycling stability. In this study, a novel cathode material with Ti-substitution on Ni site, P2-type Na0.67Ni0.25Ti0.08Mn0.67O2 has been synthesized via solid-state synthesismethod and characterized electrochemically. Na0.67Ni0.25Ti0.08Mn0.67O2 electrodes have been observed tobe highly reversible at higher voltage ranges. The electrodes have an initial discharge capacity of 125 mAhg-1and can retain around 84% of this capacity (105 mAhg-1) even after 50 cycles at 0.1C when cycled at an uppercut-off voltage of 4.3 V. Na0.67Ni0.25Ti0.08Mn0.67O2 electrodes are believed to suppress the irreversible P2-O2 transformation by diverting the charging reaction through a more reversible P2-OP4transition.
Organic carbon gel assisted-synthesis of Li1.2Mn0.6Ni0.2O2 for a high-performance cathode material for Li-ion batteries