Ultra-high energy density supercapacitors using a nickel phosphide/nickel/titanium carbide nanocomposite capacitor electrode

Abstract

The low energy density of traditional supercapacitors has strongly restricted their applications. The utilization of novel capacitor electrodes to enhance the energy densities of supercapacitors is thus of great significance. Herein, a binder-free Ni₁₂P₅/Ni/TiC nanocomposite film is synthesized and further employed as the capacitor electrode. This nanocomposite film is grown by means of a chemical vapor deposition process, where Ni₅TiO₇ nanowires and a TiO₂ layer are in situ converted into hierarchical interconnected three-dimensional (3D) Ni/Ni₁₂P₅ nanoparticles and a porous TiC matrix, respectively. Such a nanocomposite film exhibits an extremely high specific surface area and excellent conductivity, leading to its high capacitive performance. Remarkably, the multiple redox states of Ni species, namely two pairs of redox waves are observed in neutral aqueous solutions. At a current density of 10 mA cm⁻², its specific capacitance in 1 M Na₂SO₄ aqueous solution is as high as 160.0 mF cm⁻². The maximal energy density of a supercapacitor fabricated with this nanocomposite capacitor electrode is 42.6 W h kg⁻¹ at a power density of 1550 W kg⁻¹. Such an ultra-high energy density is even comparable with that of Li-batteries. The proposed supercapacitor thus has high potential for industrial applications.