Structural engineering of cathodes for improved Zn-ion batteries

Abstract

A unique 3D flower-like zinc cobaltite (ZnCo 2 O 4- x ) with oxygen vacancies is designed and fabricated and a flexible solid-state ZIB was demonstrated, which delivers an extremely stable capacity under bending states. Aqueous zinc-ion batteries (ZIBs) are attracting considerable attention because of their low cost, high safety and abundant anode material resources. However, the major challenge faced by aqueous ZIBs is the lack of stable and high capacity cathode materials due to their complicated reaction mechanism and slow Zn-ion transport kinetics. This study reports a unique 3D ‘flower-like’ zinc cobaltite (ZnCo 2 O 4- x ) with enriched oxygen vacancies as a new cathode material for aqueous ZIBs. Computational calculations reveal that the presence of oxygen vacancies significantly enhances the electronic conductivity and accelerates Zn 2+ diffusion by providing enlarged channels. The as-fabricated batteries present an impressive specific capacity of 148.3 mAh g −1 at the current density of 0.05 A g −1 , high energy (2.8 Wh kg −1 ) and power densities (27.2 W kg −1 ) based on the whole device, which outperform most of the reported aqueous ZIBs. Moreover, a flexible solid-state pouch cell was demonstrated, which delivers an extremely stable capacity under bending states. This work demonstrates that the performance of Zn-ion storage can be effectively enhanced by tailoring the atomic structure of cathode materials, guiding the development of low-cost and eco-friendly energy storage materials.