Roles of Processing, Structural Defects and Ionic Conductivity in the Electrochemical Performance of Na3MnCO3PO4 Cathode Material

Na3MnCO3PO4 with a potential to deliver two-electron transfer reactions per formula via Mn2+/Mn3+ and Mn3+/Mn4+ redox reactions and a high theoretical capacity (191 mAh/g) can play an important role in Na-ion batteries. This study investigates the dependence of the electrochemical performance of Na3MnCO3PO4-based sodium-ion batteries on processing, structural defects and ionic conductivity. Na3MnCO3PO4 has been synthesized via hydrothermal process under various conditions with and without subsequent high-energy ball milling. Particle sizes, structural defects and ionic conductivity have been studied as a function of processing conditions. It is found that Na3MnCO3PO4 nanoparticles (20 nm in diameter) can be produced from hydrothermal synthesis, but the reaction time is critical in obtaining nanoparticles. Nanoparticles exhibit a higher ionic conductivity than agglomerated particles. Further, structural defects also have a strong influence on ionic conductivity which, in turn, affects the charge/discharge capacities of the Na3MnCO3PO4-based sodium-ion batteries. These results provide guidelines for rational design and synthesis of high capacity Na3MnCO3PO4 for Na-ion batteries in the near future. (C) The Author(s) 2015. Published by ECS. All rights reserved.