New insights to build Na+/vacancy disordering for high-performance P2-type layered oxide cathodes

Abstract

P2-type Na-based layered oxides are potential cathode materials for high power Na-ion batteries (NIBs). However, complex Na+/vacancy ordering rearrangement evidenced by obvious voltage plateaus in the electrochemical profiles severely affects the Na storage capacities and cycling stability, hindering the commercialization of P2 materials. Herein, we show that the unfavorable rearrangement can be avoided by pre-forming lower Na content P2 materials with a delocalized electronic structure and modulated site energy difference between Naf and Nae, as demonstrated by DFT calculations. The disordered framework and enlarged interlayer spacing can be sustained throughout the whole electrochemical process, ensuring both a wider solid-solution region and smaller volume change during de-/sodiation. As a consequence, an excellent electrochemical performance, namely a high reversible capacity of 165.1 mAh g−1, a superior rate performance of 76.7% of capacity retention at 1000 mA g−1, and 91.7% capacity retention after 150 cycles, is harvested. Moreover, this strategy is universal and can be used to synthesize various disordering high-capacity P2 materials. This work provides a long-neglected and unexpected idea for improving the comprehensive performance of P2-type materials for facilitating their practical applications in NIBs.