Refining the electrochemical performance of Na4MnAl(PO4)3 cathode material by magnesium doping for sodium ion batteries

Na4MnAl(PO4)3 (NMAP) with cheap price, high voltage plateaus and appreciable theoretical capacity has caused growing concern as cathode for sodium-ion batteries (SIBs). But it is still burdened with the inferior ion-diffusion kinetics and the Jahn-Teller distortions, which would result in unsatisfactory capacity and rapid capacity decay. Herein, we present an Mg2+ doping strategy to conquer the above crucial obstacles and carry out a systematic investigation of how the Mg doping affect the sodium storage performance of NMAP. The findings indicate that this method endows the materials with boosted electrode reaction kinetics and structural stability. Consequently, the composites show visible enhancements in the electrochemical performance after the introduction of Mg. The optimal Mg doped sample (Mg0.10-NMAP/C) presents a high discharge capacity of 105.1 mAh g-1 and an acceptable energy density of 360.5 Wh kg- 1 at 0.1 C, as compared with those (91.4 mAh g-1 and 308 Wh kg- 1) of undoped NMAP/C. Besides, the introduction of Mg contributes to higher capacity retention after 100 cycles at 0.2 C (57.7 % for NMAP/C, vs. 73.8 % for Mg0.10-NMAP/C). Our study offers a valuable strategy to modify NMAP with improved electrochemical performance, which would accelerate its course of commercial application.