Constructing highly safe and long-life calcium ion batteries based on hydratedvanadium oxide cathodes featuring a pillar structure

Calcium-ion batteries (CIBs) have generated intense interest due to the growing demand for safer, cheaper, and large-scale energy storage systems. However, their development is still in its infancy, owing to the lack of suitable cathodes for sustaining reversible Ca²⁺ intercalation/deintercalation. Herein, layered H₂V₃O₈ (HVO) with Zn²⁺ pre-insertion (ZHVO) is reported as a high-rate and highly durable cathode material for CIBs. The existence of Zn²⁺ and H₂O pillars could expand the interlayer spacing up to 1.8 nm, which is favorable for the diffusion of bulky Ca²⁺. The formation of Zn–O bonds facilitates electron transfer and enhances electrical conduction. Consequently, the ZHVO cathode achieves superior capacity performance (213.9 mAh·g⁻¹ at 0.2 A·g⁻¹) and long lifespan (78.3% for 1,000 cycles at 5 A·g⁻¹) compared to pristine HVO. Density functional theory (DFT) calculations revealed that Zn²⁺ moved during Ca²⁺ intercalation, thereby reducing the diffusion energy barrier and facilitating Ca²⁺ diffusion. Finally, a safe aqueous calcium ion cell was successfully assembled.