Using High Valence Nb to Regulate the Superlattice Structure for the Na-Ion Layered Oxide Cathode with Superior Electrochemical Performance

It is possible to enhance energy density in sodium-ion batteries by increasing the cutoff voltage, however, high voltage operation brings challenges to the performance of cathode materials. The integration of honeycomb-like superlattice structures into cathode materials has the potential to enhance high-voltage performance; yet, the risk of irreparable structural damage occurring under extreme voltage conditions cannot be ignored. This study introduces a high valence element, Nb, in an innovative manner, using its induced elemental segregation effect, to implement a modification strategy for P2–Na0.80Li0.13Ni0.20Mn0.67–xNbxO2 superlattice structure cathodes. This strategy includes surface alkali treatment, coating layer design, sodium vacancy control, and crystal structure improvement to develop an enhanced performance cathode with a voltage range of 1.5–4.5 V. It is noteworthy that doping bring about the production of C2/m symmetric Na3NbO4 compounds with distinctive [NbO5] and [NaO5] five-coordination structures. This structures not only enhanced interfacial stability but also improves the ion transfer efficiency. The strategy increases the initial discharge specific capacity to 196.3 mA h g–1, facilitating the formation of a stable lithium manganese superlattice structure cathode capable of functioning across a broad voltage range. After 100 cycles at 0.5 C, the capacity retention rate is 88.3%, and very good rate performance (93.1 mA h g–1 at a high rate of 5 C). This study presents a new design for cathodes in sodium-ion batteries.