Enhancing rate capability of amorphous nickel phosphate supercapattery electrode via composition with crystalline silver phosphate

The performance of a supercapattery depends on its energy density, rate capability of charge and discharge and stability of electrode. Here in, a sonochemical method followed by calcination was applied to synthesize nickel phosphate-silver phosphate (Ni₃(PO₄)₂–Ag₃PO₄) nanocomposites. Morphological studies revealed that crystalline Ag₃PO₄ (∼10 nm) was intimately anchored on the surface of amorphous Ni₃(PO₄)₂, which benefits efficient charge transfer between the two metal phosphates. The optimized Ni₃(PO₄)₂–Ag₃PO₄ nanocomposite electrode exhibited a significant boost in rate capability from 29% (Ni₃(PO₄)₂) to 78% capacity retention with the maximum specific capacity of 478C/g at 1 A/g in 1 M KOH electrolyte. The enhancement of rate capability originated from a more rapid electron-transfer rate and an augmentation of electroactive sites for electrolyte ion diffusion from the interfaces of porous Ni₃(PO₄)₂ and an improvement in the electrical conductivity of crystalline Ag₃PO₄. The fabricated Ni₃(PO₄)₂–Ag₃PO₄//activated carbon-based supercapattery exhibited an energy density of 32.4 Wh/kg at 399.5 W/kg and excellent cyclic stability (∼82% capacity retention after 5000 cycles).