Unleashing O3-Type Layered Cathode Capacity via Rb-Modulation for Advanced Sodium-Ion Batteries

Optimizing the Rb modulation strategy in O3-type NaNi_0.5Mn_0.5O₂ (NaNM) layered oxides addresses the practical challenges of phase transitions and slow ion diffusion, thereby unlocking near-theoretical capacity. Even with a minute 1% Rb doping, significant improvements in specific capacity and cycling stability are observed. The Na_0.99Rb_0.01Ni_0.5Mn_0.5O₂ (NaNMR-1) sample exhibits a reversible capacity of 235.1 mAh g^-1 at 0.2 C, maintaining 93.1% capacity retention after 100 cycles in a full cell configuration (NaNMR-1||HC). Theoretical calculations and comprehensive characterizations reveal that Rb decoration enhances Na⁺ transport channels and strengthens TM-O bonds, substantially reducing the energy barrier for ion migration and improving structural reversibility. This study underscores the potential of this approach to significantly enhance the cycle stability and specific capacity of O3-type layered oxide cathodes, promising for high-performance sodium-ion batteries.