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-Na0.85Li0.12Ni0.22Mn0.66O2(P2-NLNMO) was developed. The complete solid-solution reaction over a wide voltage range ensures both fast Na(+)mobility (10(-11)to 10(-10) cm(2) 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.