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

摘要

Sodium super-ionic conductor (NASICON)-structured phosphates are emergingas rising stars as cathodes for sodium-ion batteries. However, they usuallysuffer from a relatively low capacity due to the limited activated redox couplesand low intrinsic electronic conductivity. Herein, a reduced graphene oxidesupported NASICON Na_3Cr_(0.5)V_(1.5)(PO_4)_3 cathode (VC/C-G) is designed, whichdisplays ultrafast (up to 50 C) and ultrastable (1 000 cycles at 20 C) Na~+ storageproperties. The VC/C-G can reach a high energy density of ≈470 W h kg?1 at0.2 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 activatedV~（5+）/V~（4+）, V~（4+）/V~（3+）, V3+/V2+ couples. In situ X-ray diffraction (XRD) results disclosea combination of solid-solution reaction and biphasic reaction mechanismsupon cycling. Density functional theory calculations reveal a narrow forbiddenbandgap 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 minto reach 80 state of charge. The work provides a widely applicable strategy forrealizing multi-electron cathode design for high-performance SIBs.