High-performance Na3V2(PO4)2F2.5O0.5 cathode: Hybrid reaction mechanism study via ex-situ XRD and sodium storage properties in solid-state batteries

Presently, sodium-vanadium fluorophosphates are highly competitive cathode materials for sodium ion batteries (SIBs) due to the high operating voltage and specific capacity. Herein, self-assembly Na3V2(PO4)2F2.5O0.5 microspheres with uniform polypyrrole (PPy)-coating modification ([email protected]) are successfully constructed via a facile solvothermal method combined with chemical oxidation for the first time. Benefiting from the improved reaction kinetics and large electrolyte–electrode contact area, the [email protected] composite exhibits superior rate capability (119 mAh g−1 at 0.2 C and 71 mAh g−1 at 10 C) and cycling stability (78% capacity retention after 1000 cycles) in solid-state SIBs. Importantly, the solid-state full SIBs are built based on the [email protected] as cathode and NaTi2(PO4)3 (NTP) as anode together with gel polymer electrolyte, and it presents an attractive energy density of 198 Wh kg−1 at 1 C. Moreover, the hybrid reaction mechanism mixed with two-phase transformation and solid-state reaction of [email protected] composite is investigated in detail through ex-situ XRD analysis.