Synergistic structural pillaring and phase-driven valence modulation via Ca ²⁺ /Sb ⁵⁺ co-doping for h

Ca ²⁺ /Sb ⁵⁺ co-doping optimizes P2/O3 NaNi _0.5 Mn _0.45 Mg _0.05 O ₂ cathode for high-voltage sodium-ion batteries. Ca ²⁺ expands interlayer spacing for fast Na ⁺ transport. Sb ⁵⁺ restrains Jahn–Teller distortion for stable cycling at 4.3 V.