Structure modulation strategy for suppressing high voltage P3-O1 phase transition of O3-NaMn0.5Ni0.5O2 layered cathode

Layered O3-type NaMn0.5Ni0.5O2 has been widely investigated as cathode material for sodium-ion batteries (SIBs). However, it usually suffers from detrimental phase transformation upon high voltage (>4.1 V) and sluggish Na+ migration kinetics, leading to rapid capacity decay and limited rate capability. Herein, guided by the first principles calculations, a structure modulation strategy to construct mechanically robust transition metal oxides (TMO2) layers for O3-NaMn0.5Ni0.5O2 is realized through Mg/Ti co-substitution. After Mg/Ti co-substitution, the capability of the TMO2 layers framework of O3 phase has been significantly improved to go against and tolerant strains and distortions, and thus remarkably enhanced the electrochemical performance of O3 phase upon high voltage. The as-prepared O3-type NaMn0.45Ni0.45Mg0.05Ti0.05O2 exhibits an initial discharge capacity of 177.7 mAh g−1 at a current density of 0.1 C in a voltage range of 2.0–4.2 V, and the detrimental P3-O1 phase transition upon 4.0 V can be effectively suppressed as well as the Na+ diffusion kinetics is enhanced under high voltage, subsequently leading to improved high voltage cycling-stability and rate-capability.