Alloying strategy-induced oxygen vacancies for superior potassium storage kinetics

Potassium ion batteries (KIBs) have emerged as an economical and efficient energy storage system. However, the unsatisfactory capacity of KIBs using Prussian blue as the cathode has severely hindered their further development. To address this issue, researchers have turned their attention to alternative cathode materials for KIBs, such as vanadium oxides (e.g., K 0.5 V 2 O 5 , KVO). In these vanadium-based materials, K + is stored between the layered structures of KVO. Nevertheless, our study revealed that structural collapse and sluggish electrochemical kinetics of KVO during long-term cycling impede its practical application. To overcome these challenges, we constructed oxygen vacancies to synthesize a layered electrode material K 0.5 V 2 O 5-x (denoted as KVO x ) with high structural stability. This modification significantly increased the number of electrochemical active sites, improved the K + diffusion coefficient by one order of magnitude, and thereby enhanced the reaction kinetics and overall electrochemical performance of the material. As a result, the KVO x cathode with rich oxygen vacancies delivered a reversible capacity of 120 mAh g −1 at a current density of 100 mA g −1 , and maintained a high capacity retention rate of 86.7% after 350 cycles at 500 mA g −1 . Furthermore, the reversible storage mechanism of K + in KVO x was systematically elucidated by various ex-situ characterization techniques. This study provides an effective electrode material design strategy via vacancy engineering to improve the electrochemical performance of KIBs.