Nanostructured zig-zag γ-Mo₂N thin films produced by glancing angle deposition for flexible symmetrical solid-state supercapacitors

Abstract

The performance of electrochemical capacitors strongly depends on their accessible surface area, chemical stability, and electrical conductivity. Simple columnar and zig-zag γ-Mo2N thin-film electrodes were prepared by magnetron sputtering. The latter is obtained by glancing angle deposition (GLAD), which is known for open porous structures due to the ballistic shadowing effect. As intended, the zig-zag structured γ-Mo2N electrode presents an outstanding area capacitance of 248 mF/cm2 at a scan speed of 50 mV/s, which is 4 times higher than that of the simple columnar one. Both of them exhibit excellent cycling stability of 95 % over 20,000 cycles (at 200 mV/s). The symmetrical solid-state supercapacitor prepared with the zig-zag structured γ-Mo2N thin film delivers an excellent power density of 107.1 W/cm3 at 33.8 mWh/cm3, and its volumetric capacitance is ∼ 3.5 times higher than the simple columnar structured γ-Mo2N device. Bending tests of such solid-state γ-Mo2N supercapacitors proved their mechanical flexibility to a bending angel of even 107°. Based on these studies we can conclude that the highly porous zig-zag structured γ-Mo2N-based electrodes prepared by GLAD combine outstanding electrochemical energy storage capabilities with excellent mechanical flexibility.