Intercalation design of layered vanadium phosphate based cathode material towards high-performance aqueous zinc-ion batteries

Aqueous zinc-ion batteries (AZIBs) have attracted significant attention because of high theoretical energy density, low cost, environmental friendliness and high safety. Among various cathode materials, vanadium phosphate (VOPO4) with a layered structure exhibits huge potential due to high Zn-storage capacity. However, the poor intrinsic conductivity and structural deterioration during the cycling process always result in low Zn2+ diffusion coefficient and weak reversibility. Herein, a novel potassium vanadyl phosphate (KVOPO4) cathode material was designed by the intercalation of K+ into the interlayer of VOPO4 via a simple solvothermal reaction. Benefiting from the unique layered structure and intercalation effect, the KVOPO4 electrode exhibits large discharge capacity and enhanced cycling stability (153.2 mAh g- 1 at 1 A/g after 400 cycles), and excellent rate capability (119.4 mAh g- 1 at 5.0 A/g). The electrode also suggests a pseudocapacitance controlled storage behavior with high contribution percentage of 98 % at 0.8 mV/s. Besides, ex-situ XRD and XPS were conducted to demonstrate the related phase transitions upon the Zn2+ insertion/extraction process, revealing the reversible Zn-storage mechanism of the KVOPO4. This work is expected to enrich the design strategy of VOPO4-based cathode materials and pave the exploration of high-performance AZIBs towards energy storage applications.