Polypyrrole hollow nanospheres: stable cathode materials for sodium-ion batteries.

Hollow polypyrrole (PPy) nanospheres with high sodium storage capacity as cathode materials for Na-ion batteries were reported. PPy hollow nanospheres demonstrated high current rate capacity and good cyclability. It was revealed by electrochemical testing and DFT calculation that the as-prepared PPy hollow nanospheres participate in reversible doping/de-doping reactions.