Stabilizing Layered-Type K0.4V2O5 Cathode by K Site Substitution with Strontium for K-Ion Batteries

Abstract

Developing suitable cathodes with high capacity and high power is challenging for K-ion batteries. Herein, electrochemical K-ion storage properties of the layered-type K0.4V2O5 (KVO) cathode by incorporating divalent strontium ions (Sr2+) into its crystal structure are enhanced. Divalent strontium ions (1.18 Å) are preferentially incorporated into the octahedrally coordinated K (1.38 Å) layers due to the similar ionic size compared to V4+ (0.58 Å). The introduction of 3 mmol of Sr ions in the KVO crystal improves electrical conductivity and reduces K-ion diffusion energy barriers. In addition, the strong Sr2+ and O2− interaction acts as a structural pillar, suppressing irreversible phase transition during charge–discharge process. Multi-physics simulations clearly confirm that the K0.34Sr0.03V2O5 (KS3VO) cathode exhibits a more uniform K-ion distribution and enhanced reactions of K-ions compared to the KVO cathode at various depths of discharge. As a result, the KS3VO cathode demonstrates improved reversible capacity, cycling stability, and power capability over the KVO cathode in a K-ion cell. Synchrotron X-ray analysis reveals how Sr substitution enhances the electrochemical K-ion storage properties of the KS3VO cathode. In addition, the KS3VO cathode exhibits superior thermal stability and cycling stability in a full cell coupled with a hard carbon anode compared to the KVO cathode.