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

Abstract

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.