Rationally Designed Sodium Chromium Vanadium Phosphate Cathodes with Multi‐Electron Reaction for Fast‐Charging Sodium‐Ion Batteries

Sodium super‐ionic conductor (NASICON)‐structured phosphates are emerging as rising stars as cathodes for sodium‐ion batteries. However, they usually suffer from a relatively low capacity due to the limited activated redox couples and low intrinsic electronic conductivity. Herein, a reduced graphene oxide supported NASICON Na 3 Cr 0.5 V 1.5 (PO 4 ) 3 cathode (VC/C‐G) is designed, which displays ultrafast (up to 50 C) and ultrastable (1 000 cycles at 20 C) Na + storage properties. The VC/C‐G can reach a high energy density of ≈ 470 W h kg −1 at 0.2 C with a specific capacity of 176 mAh g −1 (equivalent to the theoretical value); this corresponds to a three‐electron transfer reaction based on fully activated V 5+ /V 4+ , V 4+ /V 3+ , V 3+ /V 2+ couples. In situ X‐ray diffraction (XRD) results disclose a combination of solid‐solution reaction and biphasic reaction mechanisms upon cycling. Density functional theory calculations reveal a narrow forbidden‐band gap of 1.41 eV and a low Na + diffusion energy barrier of 0.194 eV. Furthermore, VC/C‐G shows excellent fast‐charging performance by only taking ≈11 min to reach 80% state of charge. The work provides a widely applicable strategy for realizing multi‐electron cathode design for high‐performance SIBs.