Strategic phase modulation in Na0.8(Mn-Fe-Ni)O2 system delivers high energy density and structural stability

Abstract

The growing demand for sustainable energy storage positions Na-ion batteries as a compelling, cost-effective alternative to Li-ion technology. This study investigates the impact of phase engineering on structural and electrochemical behavior in the Na0.8(Mn-Fe-Ni)O2 system, harnessing the outstanding performance characteristics of layered oxide cathodes. Samples calcined at 700 °C, 800 °C, 900 °C, and 1000 °C display diverse phase compositions, including P and O-type phases. Rietveld refinement of X-ray Diffraction (XRD) data shows that increasing Ni content resulted in reduced Na-O layer spacings, compromising rate performance. P2/O3-Na0.8Mn0.53Fe0.14Ni0.33O2, calcined at 900 °C, achieved highest discharge capacity (∼139 mAh g−1), followed by Na0.8Mn0.53Fe0.25Ni0.22O2, calcined at 800 °C (∼134 mAh g−1) at 0.1C. For constant Fe content, decreasing the Ni/Mn ratio results in sloping charge-discharge curves, indicating reduced honeycomb ordering during cycling. P2 phases formed at 1000 °C show significant capacity retention loss. Na0.8Mn0.64Fe0.14Ni0.22O2 demonstrates the best overall performance, retaining over 88 % of its initial capacity after 50 cycles at 0.2C. Operando Synchrotron XRD analysis reveals a minimal (∼-1.6 %) change in the c parameter during cycling, correlating with exceptional capacity retention. This work emphasizes the critical role of phase composition, metal ratios, and synthesis temperature in optimizing Na0.8(Mn-Fe-Ni)O2 based cathodes for high-performance Na-ion batteries. © 2025 Elsevier B.V.