Optimizing O bonding environment to improve structural stability and performance of O3-type NaNi0.5Mn0.5O2 cathode material

Abstract

O3-type sodium layered oxides are regarded as a highly suitable cathode for sodium-ion batteries (SIBs) owing to their high capacities and high compositional diversity. Nevertheless, rapid capacity decline and slow kinetics caused by complex phase transition and high tetrahedral site energy of Na+ diffusion transition state limit their practical use. Herein, we propose an effective strategy of optimizing O bonding environment to enhance the stability of the M-O bond and layered structure of the O3-type NaMn0.5Ni0.5O2 (NaMN) by Zn/Ti codoping, which has been confirmed by electrochemical tests, ex situ X-ray powder diffraction (XRD), and Rietveld refinement. As a consequence, Zn/Ti codoped O3-NaMn0.4Ni0.4Zn0.1Ti0.1O2 (NaMNZT) electrode delivers a high discharge capacity of 165.1 mAh g−1 at 0.1C, superior rate performance of 80.8 mAh g−1 at 5C, and 76.4% capacity retention after 100 cycles at 0.2C. This concept of optimizing O bonding environment affords a promising strategy for designing and constructing stable sodium ion host.