Suppressed O3–P3 phase transition of Cu/Fe/Mn-based layered oxides as cathode materials for high performance sodium-ion batteries

Abstract

O3-type Cu/Fe/Mn-based layered oxides are regarded as promising cathode materials for sodium-ion batteries due to the abundance of elements in the Earth's crust and the imperative for large-scale energy storage. However, these materials still encounter some challenges, including low capacity and insufficient rate performance. In this study, Al-doped, cobalt-free, and nickel-free Na0.9Cu0.18Fe0.3Mn0.52-xAlxO2 (x = 0, 0.03, 0.05, 0.08) are successfully synthesized by using the solid-state method to introduce non-electrochemically active elements to stabilize the crystal structure and enhance the electrochemical performance. The impact of Al-doping is comprehensively analyzed by using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), galvanostatic intermittent titration technique (GITT), and electrochemical impedance spectroscopy (EIS). Al-doping effectively enhances the diffusion coefficient of Na+, reduces the Jahn-Teller effect caused by Mn3+ and mitigates the transition from O3 to P3 phase. Finally, it stops the partial phase transitions from O3 to P3, which can be found in pristine oxide without Al-doping during charge-discharge cycling. Notably, the Na0.9Cu0.18Fe0.3Mn0.47Al0.05O2 electrode exhibits a reversible capacity of 123.89 mAh g−1 at 0.1 C, a capacity retention rate of 91.1 % after 200 cycles at 1 C, and a discharge capacity of 66.36 mAh g−1 at a high rate of 5 C.