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. (© 2022 The Authors. Advanced Energy Materials published by Wiley‐VCH GmbH)