Regulating the local chemical environment in layered O3-NaNi0.5Mn0.5O2 achieves practicable cathode for sodium-ion batteries

The O3-type layered oxides featuring sufficient Na reservoir have been extensively investigated as promising cathode candidates for sodium-ion batteries. However, the complicated phase transitions derived fast capacity decay has severely impeded its practical applications. Herein, we present a scalable yet feasible strategy to tune the local chemical environment in O3-NaNi 0.5 Mn 0.5 O 2 via Al 3+ doping for dramatically enhancing its electrochemical properties. Specifically, the modulated O3-NaNi 0.45 Al 0.1 Mn 0.45 O 2 cathode raises the capacity retention rate from 40.9% to 86.2% within 200 cycles at a current density of 85 mA g −1 . Combining theoretical calculation and experimental characterizations, it is confirmed that the Al 3+ doping induced reinforcement of transition metal-oxygen bonds and enlargement of Na layer distance can simultaneously inhibit the complicated phase transitions and decrease the Na + diffusion energy barrier, which are responsible for the impressive performance improvement. Importantly, the full-cell device based on this unique cathode and commercial hard carbon anode can deliver a high energy density of 213.5 Wh kg −1 , suggesting its great potential of practicability. This work provides a new insight in finely designing high performance layered oxide cathode for sodium ion batteries, which advances the next generation of cost-effective yet grid-level energy storage systems.