P2/O3 biphasic Ni/Fe/Mn-based layered cathode with high capacity and great cyclability for sodium-ion batteries

Abstract

The rapid capacity loss suffered by P2-type Ni/Fe/Mn-based layered cathode materials, which is caused by deleterious high-voltage phase transformations and the dissolution of active materials, greatly limits their application in large-scale sodium-ion battery installations. In this study, a novel P2/O3 biphasic Na_0.62Mg_0.05Ni_0.15Fe_0.2Li_0.05Mn_0.6O₂ (NM-NFLM) layered cathode is developed using a multi-element (Mg and Li) co-substitution strategy. The absence of significant voltage plateaus in the charge/discharge profiles of cells featuring the proposed cathode indicates that deleterious phase transformations and concomitant lattice mismatch in the high-voltage region are effectively suppressed because of the intergrown structure of the resulting cathode, which has also been demonstrated by ex-situ X-ray diffraction analyses. The optimized cathode also displays improved structural stability and enhanced Na⁺ diffusion kinetics owing to the incorporation of stabilizing dopant pillars. Hence, the assembled Na half-cell delivers a high initial capacity of 205.6 mAh g⁻¹ at 0.1 C and excellent rate capability (98.6 mAh g⁻¹ at 10 C). Moreover, the P2 phase of NM-NFLM is maintained throughout the charging and discharging processes, with only a small amount of the O3 phase undergoing reversible phase transitions of O3-P3-O3, which improves its structure stability significantly. This study presents a design and optimization strategy of high-performance Ni/Fe/Mn-based cathodes.

Graphical Abstract