Cu/Sb induced minimal lattice distortion for the development of high-performance sodium-ion battery cathode materials

O3-layered oxides are considered promising for various applications due to their high capacity. However, these O3-type materials are prone to undergo an irreversible O3-P3 phase transition, which adversely impacts their structural stability. Elemental doping has been identified as an effective strategy to mitigate this issue. However, substituting Cu at the redox center reduces the capacity of the pristine material. The unique introduction of the Sb element reduces the lattice oxygen ratio, leading to a significant increase in initial capacity. Thus, the Cu/Sb co-doped material NaNi 0.37 Mn 0.49 Cu 0.13 Sb 0.01 O 2 (NNMCS) with unique O3-dominated phase transition process, was successfully prepared using the high temperature solid-phase method. Cu/Sb doping increases Mn⁴⁺ concentration through the charge compensation mechanism at transition metal sites, mitigating the negative structural effects of the dual simplicial state e g orbitals in the high-spin Mn³⁺ state. Doping with Cu/Sb increases the electron cloud density at the transition metal sites, enhancing the electron shielding effect and ultimately causing the distance between the transition metal sites to expand. The increased distance between the transition metal sites indirectly promotes flexibility during transition metal migration, resulting in electrode materials with a smaller rate of lattice parameter change during cycling and ultimately enhancing phase transition reversibility. As a result, NNMCS demonstrates a high initial specific capacity of 188 mAh/g and 78% capacity retention after 200 cycles at 1 C within a 2.0–4.3 V window. This work provides valuable insights into the coupling mechanism between capacity and structural stability in layered oxides for sodium-ion batteries.