Effective reversible calcium/aluminum ion intercalation into VOPO4 enabled by organic molecular assistance†

Although lithium-ion batteries (LIBs) have achieved widespread adoption in the fields of communications and consumer electronics, aqueous batteries, due to their low cost and high safety, are also considered a promising technology for future sustainable energy storage. However, the high charge density of Ca²⁺ and Al³⁺ leads to a strong electrostatic interaction with the host material, which makes the selection of cathode materials for aqueous batteries an important challenge. In this paper, the interlayer spacing of the layered material VOPO₄ has been expanded by the insertion of phenylamine, and it has been successfully applied in emerging aqueous calcium-/aluminum-ion batteries. After PA intercalation, the modified materials could realize an obvious specific capacity improvement. At a current density of 0.1 A g⁻¹, it can reach an initial specific capacity of 147 mA h g⁻¹ and maintain stable cycling performance for over 800 cycles. Compared with other similar counterparts, the specific capacity and cycle stability of VOPO₄ after PA intercalation could show comprehensive advantages, which provides a novel orientation for the design of multivalent ion batteries within aqueous battery systems.