Low-Strain Cathode via Electrochemical Conversion for High-Power and Durable Aqueous Zinc-Ion Batteries

Vanadium-based compounds are promising cathodes for aqueous zinc-ion batteries (AZIBs) due to their multivalent redox chemistry and high theoretical capacity, but their cycling stability is hindered by weak interlayer interactions and strong Zn 2+ –V–O electrostatics, leading to lattice strain (volumetric strain, ∼ 20%) and high ion migration barriers. Herein, we demonstrate a simple, cost-effective, and efficient in situ electrochemical conversion strategy to transform VB 2 into Zn 3 (OH) 2 V 2 O 7 ·2H 2 O (ZnVOH), a vanadium-based cathode featuring low-strain characteristics (volumetric strain of 4.29%). ZnVOH possesses a large open and expanded framework structure, water-mediated shielding layers that weaken Zn 2+ –V–O interactions and lower migration barriers, and a [ZnO 6 ]-[VO 4 ] framework that buffers structural stress during Zn 2+ /H + insertion. Meanwhile, soluble borate species (B 4 O 7 2– and B(OH) 4 – ) generated during conversion stabilize the electrolyte pH and suppress parasitic phase formation, further enhancing durability. To improve the electronic conductivity, a carbon-coated composite (ZnVOH@C) was fabricated. Density functional theory calculations confirm its enhanced electronic transport and Zn 2+ /H + diffusion kinetics. Consequently, ZnVOH@C delivers a high reversible capacity of 422.3 mAh g –1 at 0.1 A g –1, along with ultralong cycle life and excellent capacity retention at a high rate (>80% after 8000 cycles at 10 A g –1 ). This work provides a design paradigm for developing high-capacity, durable cathodes for next-generation AZIBs.