A nickel/cobalt-free Mn-based layered oxide cathode based on an orbital hybridization modulation strategy for high energy density sodium-ion batteries

Abstract

Conventional nickel–manganese-based layered oxides, due to their high energy density, are promising cathode materials for sodium-ion batteries (SIBs). However, the relatively high cost of elements such as nickel and cobalt poses a challenge to the development of cost-effective SIBs for large-scale energy storage. To address this issue, we designed a Co/Ni-free cathode via a rational orbital hybridization modulation strategy, in which Mg is selected as the modulator to replace Ni. The substitution of nickel with magnesium not only reduces material cost but also, more importantly, enables magnesium to act as an electronic structure regulator. Guided by this design principle, combined theoretical and experimental analyses reveal that Mg²⁺ eliminates the strong and unstable hybridization present in the counterpart material Na_0.55Ni_0.1Fe_0.1Mn_0.8O₂ (NFM118). This effect broadens and improves the O 2p band, thereby lowering the energy barrier for electron transfer between Mn 3d and O 2p orbitals. This unique charge compensation mechanism, effectively suppresses the Jahn–Teller distortion and irreversible oxygen evolution. Consequently, the MFM118 cathode delivers a high reversible capacity of 180.78 mAh g⁻¹ within 1.5–4.3 V and exhibits superior rate performance and significantly enhanced cycling stability. This work highlights the advantage of orbital hybridization modulation in developing cost-effective and high-performance SIB cathodes.