Regulating Cation Interactions for Zero-Strain and High-Voltage P2-type Na2/3Li1/6Co1/6Mn2/3O2 Layered Oxide Cathodes of Sodium-Ion Batteries.

Deep sodium extraction/insertion of sodium cathodes usually causes undesired Jahn-Teller distortion and phase transition, both of which will reduce structural stability and lead to poor long-cycle reliability. Here we report a zero-strain P2- Na2/3Li1/6Co1/6Mn2/3O2 cathode, in which the lithium/cobalt substitution contributes to reinforcing the host structure by reducing the Mn3+/Mn4+ redox, mitigating the Jahn-Teller distortion, and minimizing the lattice change. 94.5% of Na+ in the unit structure can be reversibly cycled with a charge cut-off voltage of 4.5 V (vs. Na+/Na). Impressively, a solid-solution reaction without phase transitions is realized upon deep sodium (de)intercalation, which poses a minimal volume deviation of 0.53%. It attains a high discharge capacity of 178 mAh g-1, a high energy density of 534 Wh kg-1, and excellent capacity retention of 95.8% at 1C after 250 cycles.