Averting irreversible transition metal migration in O3-type NaCrO2 via oxygen vacancy defects to enable durable sodium storage

Abstract

Layered transition-metal oxides (Na_xTMO₂) are commonly studied as cathodes owing to high theoretical specific capacity and wide Na⁺ diffusion channel. The irreversible TM migration during Na⁺ de/insertion and the low actual energy density, however, are still the challenging obstacles to the practical application. NaCrO₂ (NCO), one of the typical O3-type layered oxides, has been synthesized via a spray drying-assisted solid-state reaction in this study. It experiences a highly reversible O3_hex-O’3_mon-P’3_mon phase transition during charge/discharge processes, which is primarily attributed to the effectively averted irreversible chromium migration via the in situ constructed oxygen vacancies and the accurately regulated charge cut-off voltage. Oxygen vacancies regulated NCO exhibits outstanding cyclability with capacity retention of 81.9 % after 1000 cycles at 5C in a relatively wide voltage range of 2.3–3.7 V. Our investigation ameliorates the cyclability and energy density of NCO and promotes the potential industrial application for sodium-storage layered oxide cathodes.