Inducing Na+ Site Rearrangement Through a Cosubstitution Strategy for Rapid Na Diffusion Kinetics of P2-Type Layered Metal Oxides.

ABSTRACT

The P2-layered metal oxide cathode materials are crucial for constructing high-rate sodium-ion batteries (SIBs); however, its practical application is hindered by the high Na+ diffusion barrier resulting from Na+/vacancy ordering. Herein, a Li/Zn cosubstitution P2-Na0.67Ni0.33Mn0.67O2 (NLNZM) cathode was synthesized via a sol-gel method assisted with citric acid, which can induce the rearrangement of Na+ sites to disrupt ordered structures. The XRD Rietveld refinement confirms a higher occupancy of Na+ at Nae sites with low diffusion barriers through the Li/Zn cosubstitution. In addition, the highly reversible phase evolution of the NLNZM is confirmed through in situ XRD results, thereby ensuring the stability of the structure with low volume change rate (0.78%). Furthermore, Li and Zn can reduce the surface energy and increase the interlayered distance to achieve rapid interfacial kinetics. As a result, the NLNZM has exhibited a high reversible capacity of 152.8 mAh g-1 and an outstanding rate performance of 103.4 mAh g-1 at 5C. After 200 cycles at 5C, the capacity retention rate is 81.1%. This work proposes a cosubstitution strategy to induce Na+/vacancy disorder for achieving rapid Na+ migration as a cathode material for SIBs.