Image from a scanning tunneling microscope showing the porous gold structure of the new micro-supercapacitor electrode. Image: Anaïs Ferris – LAAS.
Image from a scanning tunneling microscope showing the porous gold structure of the new micro-supercapacitor electrode. Image: Anaïs Ferris – LAAS.

Micro-supercapacitors are a promising alternative to micro-batteries because of their high power and long lifetime. Even though they have been in development for about a decade, however, until now they have stored considerably less energy than micro-batteries, limiting their usefulness.

Now, researchers in the Laboratoire d’analyse et d’architecture des systèmes (LAAS-CNRS) in Toulouse and the INRS in Quebec have developed an electrode material that allows electrochemical capacitors to match the performance of batteries, yet retain their particular advantages. This work is published in a paper in Advanced Materials.

The development of on-board electronic systems and wireless technologies is driving the miniaturization of energy storage devices. Micro-batteries are already very widespread and can store a large amount of energy due to their chemical properties. However, they are affected by temperature variations and suffer from low electric power and limited lifetime (often just a few hundred charge/discharge cycles). By contrast, micro-supercapacitors have high power and theoretically infinite lifetime, but only store a low amount of energy.

Micro-supercapacitors have been the subject of an increasing amount of research over the past 10 years, but no concrete applications have come from this research. Their lower energy density (the amount of energy they can store in a given volume or surface area) has prevented them from powering sensors or microelectronic components. Researchers in the Intégration de systèmes de gestion de l’énergie team at LAAS-CNRS, in collaboration with the INRS of Quebec, have now succeeded in overcoming this limitation by combining the best of micro-supercapacitors and micro-batteries.

They have developed an electrode material whose energy density exceeds all previous electrodes. This new electrode is made of an extremely porous gold structure doped with ruthenium oxide, which is synthesized using an electrochemical process.

"The extent of the electrode's surface and the presence of pores of various sizes are key to a large storage capacity," explains INRS professor Daniel Guay, one of the corresponding authors on the paper. "We designed this new 3D electrode using an electrochemical process to synthesize a very porous gold structure. Ruthenium oxide, a pseudo-capacitative material featuring high electrical conductivity and very good cyclability, was then inserted into the structure, resulting in unsurpassed energy density. For this type of application, component sizes are reduced to a few square millimeters, making it possible to use such expensive materials."

With this electrode, the researchers were able to produce a micro-supercapacitor with an energy density of 0.5 J/cm². This is around 1000 times greater than existing micro-supercapacitors and very similar to the density characteristics of current lithium-ion micro-batteries. When combined with their long lifetime, high power and tolerance to temperature variations, this new energy density could allow micro-supercapacitors to be used in wearable, intelligent, on-board microsystems.

This story is adapted from material from CNRS and INRS, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.