Ni(HCO 3 ) 2 nanosheet/nickel tetraphosphate (Ni(P 4 O 11 )) nanowire composite as a high-performance electrode material for asymmetric supercapacitors

Nickel compounds, especially Ni(HCO 3 ) 2 (here denoted as NiC), have been widely combined with other materials to obtain composites with a more favorable structure that exhibit excellent electrochemical performance as supercapacitors. Unfortunately, the complicated processes for preparing such composites directly restrict their further application. Herein, we prepared a NiC/nickel tetraphosphate (Ni(P 4 O 11 )) nanocomposite (NiC/NiP) by introducing H 2 PO 4 − ions into the NiC reaction system; this composite can be applied in high-performance supercapacitors. The micromorphology of NiC/NiP material displayed an appropriate combination of NiP nanowires and thin NiC nanosheets, which provide sufficient active sites, short ion diffusion paths and fast ion diffusion speeds. NiC/NiP material exhibited an excellent rate performance of 70.2% retained capacity, although the current was increased by 15 times (1196 F g −1 at 2.0 A g −1 and 840 F g −1 at 30 A g −1 ). The energy density of a NiC/NiP//active carbon (AC) asymmetric supercapacitor fabricated in 6 M KOH was as much as 39.02 W h kg −1 and 26.67 W h kg −1 under corresponding power densities of 160 W kg −1 and 8000 W kg −1 , respectively. The asymmetric supercapacitor delivered a stable cyclic performance of 78% capacitive retention after 5000 continuous charge/discharge cycles. More importantly, a 2.5 V light-emitting diode was lit successfully by two NiC/NiP//AC asymmetric supercapacitors in series. These results confirm that NiC/NiP nanocomposite has great potential in practical applications of electrochemical energy storage devices.