Decoupling slab gliding and lattice contraction in Na layered oxides to enable high-voltage Na-ion batteries

Layered transition metal oxide cathodes (NaxTMO2) demonstrate a classic type of cathode for Sodium-ion batteries (SIBs), however their practical application faces a long-standing challenge of irreversible phase transitions at high voltages, which causes unsatisfied specific energy and cycling stability, particularly for P-type (Na+ located at prismatic sites) cathodes. This phenomenon is conventionally ascribed to the Na+ re-coordination from prismatic to octahedral (O-type) configuration upon Na+ extraction, whereby the TMO2 slab gliding and abrupt c-lattice change are always coupled, and a straightforward solution to this situation remains elusive. Here, we reveal that, the TMO2 slab gliding and the lattice contraction can be decoupled, and the rapid lattice contraction under high state-of-charge underlies the fundamental origin for the irreversible phase transitions. By pre-engineering 15.8% O-type stacking faults to a P-type Na0.7Mn0.8Ni0.2O2, the dramatic volume variation and irreversible phase transitions at high voltage (4.5 V vs. Na+/Na) can be primarily eliminated. This work advances the understanding on the phase transitions at deep desodiation states, and paves up a feasible way to realize high-energy layered oxides. Phase transitions in Na layered transition metal oxide materials involving slab gliding and considerable lattice parameter changes limit the battery cycling life, especially at high voltages. Here, authors pre-engineer 15.8% O-type stacking faults to a P-type Na0.7Mn0.8Ni0.2O2, improving stability and enabling an electrode specific energy of 635 Wh kg-1 with 600-cycle life.