Sodium manganese oxide with divalent Ni in prismatic sites, represented as o-Na_0.67[Ni_0.05Mn_0.95]O₂, shows high capacity with excellent cyclability.

Lithium was substituted on the alkali site of an O3-type layered structure as cathode material for sodium-ion batteries (SIBs). Role of Li in Na intercalation and high performance is reported for the first time. The behavior of Na during intercalation is a critical factor that determines electrochemical performance. Although transition-metal oxides with layered structures have been studied extensively for SIBs, the focus has been on substitution at transition metal sites rather than at the alkali site. Here, substitution of Li at the alkali site of Na_x[Fe_yMn_1−y]O₂ (0 ≤ x, y ≤ 1) layered materials is reported for the first time. The substituted element at the alkali site can directly interfere with the behavior of Na during intercalation. In situ XRD, synchrotron powder XRD, neutron powder diffraction, ex situ XANES, and DFT calculation revealed that Li at alkali sites stabilized the layered structure during the electrochemical reaction and assisted Na intercalation by lowering the energy barrier for Na-hopping. Contrary to common understanding, Li substituted material showed an improved cyclic and rate performance in spite of the smaller interlayer spacing of the O3-type layered structure. The result provides new insight into the role of a substituted element at the alkali site and shows that the Li at the alkali site is a key factor for achieving high performance of a layered cathode material.

Na₃V₂O_2X(PO₄)₂F_3−2X–rGO with CMC binder shows the enhanced electrochemical performance; it exhibits 98% capacity retention at 0.1C rate over 250 cycles. Also, it remits discharge capacity of 98 mA h g⁻¹ at 0.2C in a full cell with a NaTi₂(PO₄)₃–MWCNT.

Apart from conventional redox chemistries, exploring high-voltage anionic redox processes, such as pure oxygen or high-valent transition metal ion redox, poses challenges due to the instability of O nonbonding or O-dominant energy states. These states are associated with destructive behaviors in layered oxide cathodes, including local structural distortion, cationic disordering, and oxygen gas evolution. In this study, we suppress first-cycle voltage hysteresis and irreversible O ₂ evolution in Li-rich oxide cathodes through covalency competition induced by the substitution of electropositive groups. We found that the nonequivalent electron distribution within an asymmetric M _A -O-M _B backbone (metal-to-metal charge transfer via oxygen ligands) increases electron density on electronegative transition metal ions, preventing them from reaching unstable oxidation states within an operating voltage range. This phenomenon is observed across diverse transition metal combinations, providing insights into controlling unnecessary oxygen redox activity. Our findings open new avenues for controlling intrinsic redox chemistry and enabling the rational design of high–energy density Li-rich oxide cathodes.