Rigid Flexible Pillaring via Synergistic Co-Doping Stabilizes High-Capacity Sodium Layered Oxide Cathode

O3-type layered oxide cathodes offer high energy density but suffer from interlayer gliding and oxygen release at elevated voltages, leading to rapid capacity fade. Here, we propose a rigid-flexible coupled pillaring strategy, where Mg/Li co-doping offers a versatile route to achieve excellent performance at high voltage. This stems from rigid Mg─O pillaring that suppresses slab gliding, together with compliant Li─O buffering that smooths the in-plane potential. In tandem, closed-shell Mg/Li weakens TM─O eg* antibonding and downshifts the O-2p band center, promoting a tempered, reversible anionic-redox reaction, thereby avoiding the usual trade-off in which improvements in durability come at the expense of capacity. Consequently, this pair redirects the high-voltage response from P3→OP2 to a P3 solid solution, cutting c-axis breathing to ∼1.7%, and the cathode delivers a capacity of over 160 mAh g^-1 at 4.2 V, retains 80% after 500 cycles at 5C. Furthermore, the cathode is scalable to kilogram batches. With excellent coin and Ah-scale pouch-cell performance, it shows guidance of design and commercial promise for high-voltage O3-type cathodes.