Ball mill assisted synthesis of Na₃MnCO₃PO₄ nanoparticles anchored on reduced graphene oxide for sodium ion battery cathodes

Na₃MnCO₃PO₄ (NMCP) particles were synthesized via ball milling of Mn(NO₃)₂.4H₂O, Na₂HPO₄.2H₂O and Na₂CO₃.H₂O powders. The particles were anchored onto reduced graphene oxide (rGO) sheets during hydrothermal reduction process under stirring. Materials produced were characterized by x-ray diffraction (XRD), Raman spectroscopy, field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), thermogravimetric (TG) measurement and galvanostatic charge/discharge tests. Results showed that dissolution of ball milling products in DI water is an effective method for separation of NMCP from byproducts. Best milling time for production of pure NMCP of minimum particle aggregation was 60 min. After preparing the composite, the needle-like NMCP particles of ∼15 nm diameter were anchored onto rGO sheets. As a promising cathode candidate for Na-ion batteries, NMCP and NMCP/rGO electrodes displayed initial capacities of 103 and 141 mAh g⁻¹ at C/30 rate with capacity retention of 71% and 81% after 15 cycles, respectively. Improvement of the cycling performance at higher rates attributed mainly to the extremely fine NMCP nanoparticles and their almost uniform distribution on rGO conducting network which resulted in electronic and ionic conductivity enhancement and therefore improved the reversibility of intercalation/deintercalation reactions.