Ultrathin Nanosheet-Assembled, Phosphate Ion-Functionalized NiO Microspheres as Efficient Supercapacitor Materials

In this work, ultrathin nanosheet-assembled, phosphate ion-functionalized NiO (P-NiO) microspheres were prepared via a facile hydrothermal reaction and subsequent thermal annealing. The formation mechanism of the precursor and the resulting P-NiO microspheres is investigated in detail via condition-dependent experiments. It is observed that the P-NiO microspheres are constructed by plenty of two-dimensional (2D) ultrathin nanosheets with a thickness of about 4 nm. Meanwhile, this material also exhibits poor crystallinity with a high content of phosphate ions that homogeneously disperse throughout the microspheres. Resulting from the unique crystal feature and hierarchical microstructure, these P-NiO microspheres could deliver a specific capacity of 631.8 C·g–1 at 1 A·g–1 and long-run cycling stability with a specific capacity retention of 95.2% after 4000 charge/discharge cycles. The asymmetric supercapacitors assembled by P-NiO microspheres and active carbon could exhibit high power and energy densities (53.4 Wh·kg–1 at 0.8 kW·kg–1) and excellent cycling stability.