Oxygen defect engineering endows Co3O4 nanosheets with advanced aluminum ion storage

Atomic-level structure modulation is an effective way to boost ionic diffusion kinetics and improve the cycling stability. To relieve the strong coulombic ion–lattice interactions originating from trivalent Al3+ ions, herein oxygen-deficient Co3O4−x porous nanosheets are fabricated via a facile NaBH4 reduction strategy using a metal–organic framework template. Electrochemical kinetics analysis and theoretical calculation results reveal good pseudocapacitive property, appropriate diffusion capability and Al3+ formation energy, corroborating fast Al3+ ion storage/release kinetics and high Al3+ storage capacity. Specifically, Co3O4−x porous nanosheets exhibit a high reversible capacity of 442.3 mA h g−1 at 1.0 A g−1 and retain 104.2 mA h g−1 after 1800 cycles, remarkably higher than those of the previously reported Co3O4-based cathode materials. Furthermore, ex situ analyses reveal the conversion reaction mechanism of the Co3O4−x cathode, followed by its high structural stability upon extended cycling.