Hydrothermal Synthesis of Nickel Phosphate Nanorods for High‐Performance Flexible Asymmetric All‐Solid‐State Supercapacitors

Ni 20 [(OH) 12 (H 2 O) 6 ][(HPO 4 ) 8 (PO 4 ) 4 ]·12H 2 O nanorods are successfully synthesized via a one‐pot hydrothermal reaction. A high‐performance flexible asymmetric all‐solid‐state supercapacitor based on the obtained Ni 20 [(OH) 12 (H 2 O) 6 ][(HPO 4 ) 8 (PO 4 ) 4 ]·12H 2 O nanorods (positive electrode) and graphene nanosheets (negative electrode) is successfully assembled. It is the first report of this nanomaterial applied for all‐solid‐state supercapacitors. Interestingly, a maximum volumetric energy density of 0.446 mW h cm −3 at a current density of 0.5 mA cm −2 and a maximum power density of 44.1 mW cm −3 at a current density of 6.0 mA cm −2 are achieved by the as‐assembled device. What's more, the device also shows excellent mechanical flexibility and little capacitance change after over 5000 charge/discharge cycles at a current density of 0.5 mA cm −2 .