Sputtered Titanium Nitride Films on Titanium Foam Substrates as Electrodes for High-Power Electrochemical Capacitors

Electrochemical capacitors (ECs) with high-power capabilities and stable cycling can effectively improve the state of the art in power delivery and energy storage. In this study, we investigate reactively sputtered titanium nitride (TiN) electrodes on three-dimensional (3D) substrates with various electrolytes and high-rate cycling conditions. The electrode exhibits cycling stability with negligible capacitance fading after 5 000 cycles and a great rate capability, allowing the (dis)charge rate to extend from 0.1 to 10 V s⁻¹ and retaining nearly 50 % of the capacitance in a three-electrode system. A symmetric device made with such electrodes is capable of working at a scan rate up to 100 V s⁻¹, yielding a remarkable power density of 4.81×10⁵ W kg⁻¹ at 1.60 Wh kg⁻¹. The energy density can be pushed to 168.03 Wh kg⁻¹ at 4.03×10⁴ W kg⁻¹ by replacing the aqueous electrolyte with an organic one, and this can likely be further increased by electrolyte optimization. The material synthesis and device processing suggest that 3D TiN structures can enable a new class of high-power ECs with enhanced stability compared to their carbon- and pseudo- counterparts.