Thin Film Electrodes for Fast Electrochemical Micro-Supercapacitors

Abstract

Miniaturized power sources are key devices to get autonomous smart and connected sensors[1,2]. To reach this goal, the current trend is to fabricate micro-storage unit such as micro-batteries (MB) or micro-supercapacitors (MSC) at the wafer level. While binder or conducting agents are requested for bulk electrode synthesis, thin-film deposit technologies such as magnetron sputtering (MS) or atomic layer deposition (ALD) are versatile tools to provide binder free electrode that can be easily transferred to pilot production line. Moreover, this suitable technology is really attractive to study the intrinsic properties of electrode material for micro-devices. In this talk, we will show our recent results dealing with Nb2O5 and VN thin films deposited by MS or ALD either for planar or 3D micro-devices. Transition metal oxides thin films like RuO2 or MnO2 have been intensively studied[3–5] for MSC due to their pseudocapacitive properties. To improve the energy density of such MSC, moving from symmetric to hybrid micro-devices without scarifying the fast electrochemical process of the proposed system seems to be an interesting but challenging way from technological point of view. The electrochemical properties of the bulk Nb2O5 recently investigated[6–8] by B. Dunn et al have shown a fast pseudo-intercalation process of the lithium ion below 2 V vs Li/Li+ in orthorhombic T-Nb2O5. We have carried out in-depth study of Nb2O5 thin film to study the relationships between the synthesis parameters, the crystal structure and the electrochemical properties of this material. During the last ten years, transition metal nitride[9–11] have been investigated as an alternative for MSC electrode based on pseudocapacitance charge storage process due to their high electrical conductivity and anti-corrosion properties. We will show during this talk the preparation of vanadium nitride thin films with fine-tuned electrical, structural and electrochemical properties. Symmetric interdigitated MSC have been fabricated using microfabrication technique and tested in aqueous and protic ionic liquids electrolytes and the performance will be reported. The objective of these studies is to clearly find the suitable technology allowing to propose the fabrication of high areal energy density, small footprint area symmetric MSC or hybrid micro-devices before moving toward solid state configuration using ionogel technology.