Sodium superionic conductor (NASICON)-Na4 VMn(PO4 )3 (NVMP) cathode is attractive for sodium-ion battery application due to its reduced cost and toxicity, and high energy density (≈425 Wh kg-1 ). However, it exhibits significant polarization, limited rate and cycling performances due to its lower electronic conductivity and formation of Jahn-Teller active Mn3+ during cycling. In this report, a chemical approach is presented to partially replace Mn2+ of the NVMP framework by Mg2+ and Al3+ substitutions. The Mg- and Al-substituted NVMP cathodes present smoother voltage profiles, facile sodium (de)intercalation, enhanced rate performances (80 mA h g-1 at 5C rate) and capacity retention (≈96% after 100 cycles) in comparison with the unsubstituted sample. Their enhanced performances are attributed to suppressed Jahn-Teller effect, increased covalent character and sodium ion vacancies of the NASICON framework. These results highlight the significance of fine tuning the chemical compositions to attain high performance NASICON cathodes.
Keywords: NASICON; chemical substitution; phosphates; sodium-ion batteries.
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