The Synergistic Effect of Mg2+ and K+ in Layered-Oxide Cathode Materials for Sodium-Ion Batteries

This work studies KxFe0.2Mn0.8-yMgyO2 (y = 0, 0.05, 0.10, 0.15, namely) layered oxides as the cathode of sodium -ion battery and proposes an Mg2+-K+ synergistic effect. The previous work have proved that both K+ interca-lation and Mg2+ doping can increase the diffusion coefficient of Na+ in layered-oxide cathode materials. On this basis, this paper further demonstrates that Mg2+ doping significantly inhibits the transformation of the layered oxide to the amorphous phase, improves the stability of the layered structure, and further suppresses the loss of K+, thus improving the capacity, rate performance, and cycling stability of the material. Specifically, Mg2+ can selectively anchor K+, thereby reducing the loss of K+ during the charge-discharge process. The specific capacity of P3-KxFe0.2Mn0.7Mg0.1O2 has reached 158.8 mAh g-1, and 69.6 mAh g-1 at 0.5 C and 5 C, and the capacity retention reaches 79.1% after 200 cycles at 3 C.