Optimization of synthesis parameters for O3-type NaNi0.33Fe0.17Mn0.5O2 Na-ion battery cathode materials

Layered transition-metal oxides are promising materials for sodium-ion battery cathodes, although their electrochemical performance is very sensitive to the synthesis conditions, which dictate phase composition and particle morphology. Here, we systematically investigate the influence of two key precursor co-precipitation parameters on the structural, morphological, and electrochemical properties of NaNi0.33Fe0.17Mn0.5O2 layered oxides: temperature (40 and 60 °C) and reaction time (9 and 24 h). Upon synthesis, temperature primarily influences particle agglomeration and crystallinity, while reaction time primarily regulates particle size and phase formation. Short synthesis times combined with higher temperatures favor the formation of an O3-dominant lattice with reduced aggregation, whereas longer times promote smaller particles and the development of mixed O3/P2 phases. Electrochemical characterization reveals that the sample obtained after co-precipitation at 60 °C for a shorter duration exhibits the best rate capability, reaching a specific capacity of 130 mAh g–1 at 0.1 C, and full capacity recovery at 0.4 C after C-rate test. Conversely, samples with a mixed O3/P2 phase exhibit better structural stability, retaining up to 70% of the initial capacity after 200 cycles. The novelty of this work lies in systematically decoupling co-precipitation parameters and directly correlating them with phase evolution and electrochemical performance. These results provide clear guidance for the controlled design of high-performance sodium-ion battery cathode materials.