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

Abstract

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-NaNi0.5Mn0.5O2 via Al3+ doping for dramatically enhancing its electrochemical properties. Specifically, the modulated O3-NaNi0.45Al0.1Mn0.45O2 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 Al3+ 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.