Effect of Al3+ and Sc3+ Substitutions on the Structural and Electrochemical Properties of Nasicon-Na3mn1-Xmxti(Po4)3 (M=Sc3+, Al3+; X=0.01-0.1) Cathodes for Sodium-Ion Batteries

Trivalent cations (M=Sc3+, Al3+) with different contents (x=0.01, 0.03, 0.05, 0.07, 0.1) were incorporated for manganese in the Na3Mn1-xMxTi(PO4)3 (NMTP), yielding enhanced rate performance and capacity retention. Successful doping of these cations in the NMTP structure was confirmed by powder X-ray diffraction (PXRD) and energy dispersive X-ray spectroscopy (EDS) techniques. Impedance spectroscopy (EIS) and galvanostatic intermittent titration technique (GITT) suggests that appropriate-level doping has significantly increased the electrical conductivity and Na ion migration of the NMTP matrix. Na3Mn0.95Sc0.05Ti(PO4)3(capacity of 123 mA h g-1 at 0.2C) demonstrate the highest discharge capacity and Na3Mn0.95Al0.05Ti(PO4)3 (capacity rentention of 91% after 500 cycles at 1C) demonstrate the greatest electrochemical stability. More importantly, Na3Mn0.95M0.05Ti(PO4)3 (M=Sc3+, Al3+)//hard carbon full cells also demonstrates ideal electrochemical properties. The presented work analyzes the effects of Al3+ and Sc3+ doping in relation to the electrochemical properties of the NASICON-type structure, which will be helpful to analyze the influence of trivalent metal elements with different ionic radius and electronegativity on Mn site doping of NASICON type materials.