Electrochemical energy storage devices, particularly rechargeable batteries, are attractive solution to balance energy production of intermittent natural sources such as wind and solar. Despite its success in portable electronics market, Li-ion technology faces serious hurdle for grid storage application due to scarcity and geographical access of lithium sources. From the viewpoint of cost and abundance of raw materials, sodium ion batteries are appealing for grid storage application.1 Various classes of Na-ion electrode and electrolyte materials have been developed recently based on the know-how knowledge gained from Li-ion chemistry. However, the commercialization of NIBs has been impeded by the lack of high energy density cathodes. To this end, multi-electron based polyanionic cathodes are attractive, because of their high insertion voltages and storage capacities.2 Among the cathode materials, NASICON type cathodes with a general chemical formula NaxMM’(PO4)3(x= 2-4; M=V, Ti, Fe, Cr; Mʹ =Mn, Co, Mg, Fe) have garnered significant interest due to higher sodium ion conductivities as well as enhanced chemical and thermal stabilities.3 In this talk, we will present our recent studies on the impact of Mg2+ and Al3+ cationic substitution into the Na3V2(PO4)3 framework.4,5 The Mg- and Al-substituted NVMP cathodes exhibit smoother voltage profiles, facile sodium (de)intercalation, enhanced rate performances (80 mA h g-1 at 5C rate) and better capacity retention (~96% after 100 cycles) compared to the unsubstituted sample. Their improved performances are attributed to suppressed Jahn-Teller effect, enhanced covalent character and Na-ion vacancies created in the NASICON framework.