Realizing the Multi-electron Reaction in the Na 3 V 2 (PO 4 ) 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 H 2 PO 4 - can be used as the charge carrier for Na 3 V 2 (PO 4 ) 3 under an aqueous electrolyte, which enabled the V 3+ /V 4+ and V 4+ /V 5+ multielectron reactions in the Na 3 V 2 (PO 4 ) 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 V 5+ -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.