Oxygen defect engineering endows Co 3 O 4 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 Al 3+ ions, herein oxygen-deficient Co 3 O 4− x porous nanosheets are fabricated via a facile NaBH 4 reduction strategy using a metal–organic framework template. Electrochemical kinetics analysis and theoretical calculation results reveal good pseudocapacitive property, appropriate diffusion capability and Al 3+ formation energy, corroborating fast Al 3+ ion storage/release kinetics and high Al 3+ storage capacity. Specifically, Co 3 O 4− 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 Co 3 O 4 -based cathode materials. Furthermore, ex situ analyses reveal the conversion reaction mechanism of the Co 3 O 4− x cathode, followed by its high structural stability upon extended cycling.