Influence of precursor selection on the structural integrity and electrochemical performance of α‐NaMnO₂ cathode

Abstract In this study, the α‐NaMnO 2 phase was successfully synthesized using three different combinations of starting materials: Na 2 O 2 /Mn 2 O 3 , Na 2 O 2 /MnO 2 , and Na 2 CO 3 /Mn 2 O 3 . A one‐step heat treatment at 900°C for 5 h under air with quenching was applied. X‐ray diffraction analysis confirmed the formation of pure α‐NaMnO 2 phase in all three samples, with only slight variations in lattice parameters. Elemental and oxidation state analyses were conducted using X‐ray photoelectron spectroscopy (XPS), scanning electron microscopy with energy‐dispersive X‐ray spectroscopy, and inductively coupled plasma measurements. XPS results revealed noticeable differences in Mn ion valence states, suggesting variations in oxygen stoichiometry and the presence of oxygen‐excess structures. Electrochemical evaluations were performed in both half‐cell and full‐cell configurations. The samples exhibited distinct performance characteristics, with capacity fade over 100 cycles at C/3 between 1.5 and 4.3 V measured at 83.6%, 73.9%, and 83.1%, respectively. These differences correlated with the average oxidation state of Mn and O content. Full‐cells, paired with presodiated commercial hard carbon anodes, showed the highest capacity for the Na 2 O 2 /MnO 2 system and the best retention for the Na 2 CO 3 /Mn 2 O 3 sample. Overall, this work demonstrates how even small variations in starting materials can significantly influence the structural and electrochemical behavior of α‐NaMnO 2 .