Ni3Si2@TiO2 furs for supercapacitors with extremely high areal density and high cycleability

Abstract Supercapacitors with high energy density, fast charging/discharging rate, and long cycle life are ideal energy storage devices. A sufficient amount of the electrode materials is important to obtain high energy density supercapacitors. The poor electronic and ionic conductivity are accompanying with increasing amount of electrode materials, which hinder the energy density and capacitance retention of supercapacitors especially under high current densities. Long Ni3Si2 nanoarrays with higher areal density and larger exposed surface areas have been in situ grown on Ni foams as Ni3Si2 furs by low pressure chemical vapor deposition to give sufficient amount of electrode materials with high electronic and ionic conductivity. Atomic layer deposition process has then been adopted to coat the Ni3Si2 nanowires with different thick TiO2, yielding Ni3Si2@TiO2 furs. The Ni3Si2@TiO2 furs with 1 nm TiO2 coating have been demonstrated to have high supercapacitor performance. An extremely high specific capacitance as high as 7.82 F cm−2 has been achieved by Ni3Si2@TiO2-1nm furs at a current density of 5 mA cm−2. A high areal capacitance of 5.91 F cm−2 and an excellent cycling stability of 95.6% retention after 5000 cycles at a high current density of 100 mA cm−2 have been obtained. The asymmetric supercapacitor assembled with Ni3Si2@TiO2-1nm exhibits volumetric energy density of 1.528 mWh cm−3 at a power density of 25 mW cm−3 and 0.93 mWh cm−3 at 0.1 W cm−3.