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-Na Li Ni Mn O (P2-NLNMO) was developed. The complete solid-solution reaction over a wide voltage range ensures both fast Na mobility (10 to 10  cm  s ) and small volume variation (1.7 %). The high sodium content P2-NLNMO exhibits a higher reversible capacity of 123.4 mA h g , superior rate capability of 79.3 mA h g 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.