Synergistic Interlayer Engineering and Voltage-Regulated Self-Optimization of Sr-Doped CaV ₄ O ₉ Cathode for Ultra-Stable Aqueous Zinc-Ion Batteries

Meeting the growing demand for grid-scale energy storage requires rechargeable batteries that are inherently safe, sustainable, and cost-effective. Despite the promising prospects of aqueous zinc-ion batteries (AZIBs), their practical application is hampered by the structural instability and poor cycling stability of vanadium-based cathode materials, which remain one of the most attractive host materials for reversible Zn 2+ energy storage. Herein, this work proposes a synergistic strategy combining strontium substitution with in situ structural self-optimization to develop a high-performance Ca 0.9 Sr 0.1 V 4 O 9 (CaSrVO) cathode. The substitution of Ca 2+ with larger Sr 2+ ions expands interlayer spacing, reducing Zn 2+ diffusion barriers while maintaining the host structure through pillar stabilization. Crucially, electrochemical activation at 1.5 V triggers partial extraction of interlayer Ca 2+ /Sr 2+, thereby alleviating steric hindrance for Zn 2+ intercalation and creating additional active sites for Zn 2+ storage, while the retained Sr 2+ /Ca 2+ ions act as structural pillars to suppress amorphous phase transitions, ensuring robust structural integrity during repeated Zn 2+ intercalation/deintercalation. This synergistic approach reconciles the expanded ion diffusion pathways and reinforced structural stability, which enables CaSrVO to achieve a remarkable specific capacity of 392.9 mAh g –1 at 0.1 A g –1, significantly outperforming the pristine CaV 4 O 9 (CaVO). More importantly, the cathode demonstrates exceptional long-term cyclability, retaining 85% of its initial maximum capacity after 5000 cycles at 5 A g –1 . This work highlights the effectiveness of interlayer engineering coupled with dynamic self-optimization in unlocking the full potential of layered vanadium oxides for practical AZIB applications.