The electrochemical performance of Ta2O5 thin films in ionic liquid and ionogel electrolytes

• An innovative micro hybrid capacitor is realized using Ta2O5 thin films and MnO2 composite electrodes. • This devices has been successfully tested in ionic liquid and ionogel electrolytes. • The device provides a cell voltage 20 v and cycles stable up to 5000 mV s-1. • 2000 cycles at 500 mV s-1 have been reached. • The performance of ionic liquid and ionogel is very comparable highlighting the promising application of ionogels even for miniaturized high power devices. In this work, we present a new cell design for miniaturized energy storage devices by realizing a hybrid micro-capacitor, which uses for the first time a TaN/ Ta 2 O 5 thin film electrode in combination with a MnO 2 composite electrode. In this proof of concept study, the electrochemical performance of the dielectric material Ta 2 O 5 was of main interest. Therefore, various tantalum oxide films with different thicknesses from 23 to 80 nm have been tested in combination with a pseudocapacitive oversized MnO 2 composite electrode. This was done with two model electrolytes, namely the ionic liquid Emim FSI and the solid-state ionogel Emim FSI: PVdF 80:20. Surface capacitance values up to 1.94 µF cm -2 in Emim FSI and 2.84 µF cm -2 in IG Emim TFSI: PVdF 80:20 have been reached at high scan rates (100 mV s -1 ) with no significant distortion of the voltammograms. When films of 47 and 80 nm thickness of Ta 2 O 5 are used, stable cycling with scan rates of up to 5000 mV s -1 at a cell voltage of 20 V can be achieved even in solid-state ionogel electrolyte. This performance highlights the promising characteristics of these materials and cell concept for miniaturized high power energy storage application and opens the way for further investigations to improve this needed technology.