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