Roles of Processing, Structural Defects and Ionic Conductivity in the Electrochemical Performance of Na₃MnCO₃PO₄Cathode Material

Na 3 MnCO 3 PO 4 with a potential to deliver two-electron transfer reactions per formula via Mn 2+ /Mn 3+ and Mn 3+ /Mn 4+ 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 Na 3 MnCO 3 PO 4 -based sodium-ion batteries on processing, structural defects and ionic conductivity. Na 3 MnCO 3 PO 4 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 Na 3 MnCO 3 PO 4 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 Na 3 MnCO 3 PO 4 -based sodium-ion batteries. These results provide guidelines for rational design and synthesis of high capacity Na 3 MnCO 3 PO 4 for Na-ion batteries in the near future.