Realizing the Multi-electron Reaction in the Na₃V₂(PO₄)₃ Cathode via Reversible Insertion of Dihydrogen Phosphate Anions

Dual-ion battery (DIB) is an up-and-coming technology for the energy storage field. However, most of the current cathodes are still focused on the graphite hosts, which deliver a limited specific capacity. In this work, we demonstrated for the first time that H₂PO₄^– can be used as the charge carrier for Na₃V₂(PO₄)₃ under an aqueous electrolyte, which enabled the V³⁺/V⁴⁺ and V⁴⁺/V⁵⁺ multielectron reactions in the Na₃V₂(PO₄)₃ electrode. The fabricated aqueous DIB delivers a high average voltage of ∼0.75 V (vs Ag/AgCl) and a high capacity of 280.7 mA h g^–1. Moreover, the formed V⁵⁺-based novel cathode exhibits a capacity of 170.2 mA h g^–1 in an organic sodium-ion battery. This study may open a new direction for fabricating high-voltage electrodes through the design of DIBs.