Realizing Complete Solid‐Solution Reaction in High Sodium Content P2‐Type Cathode for High‐Performance Sodium‐Ion Batteries

P2-type layered oxides suffer from an ordered Na+ /vacancy arrangement and P2→O2/OP4 phase transitions, leading them to exhibit multiple voltage plateaus upon Na+ extraction/insertion. The deficient sodium in the P2-type cathode easily induces the bad structural stability at deep desodiation states and limited reversible capacity during Na+ de/insertion. These drawbacks cause poor rate capability and fast capacity decay in most P2-type layered oxides. To address these challenges, a novel high sodium content (0.85) and plateau-free P2-type cathode-Na0.85 Li0.12 Ni0.22 Mn0.66 O2 (P2-NLNMO) was developed. The complete solid-solution reaction over a wide voltage range ensures both fast Na+ mobility (10-11 to 10-10 cm2 s-1 ) and small volume variation (1.7 %). The high sodium content P2-NLNMO exhibits a higher reversible capacity of 123.4 mA h g-1 , superior rate capability of 79.3 mA h g-1 at 20 C, and 85.4 % capacity retention after 500 cycles at 5 C. The sufficient Na and complete solid-solution reaction are critical to realizing high-performance P2-type cathodes for sodium-ion batteries.