New types of electrodes for high-performance micro-supercapacitors

The energy autonomy of mobile electronics relies essentially on batteries, whose performance has been steadily increasing over the last few decades. For consumer products (smartphones, tablets, cameras, portable music players, etc.), the main remaining drawbacks are weight, recharging frequency and lifespan.

Another field of application where energy autonomy is much more critical is that of autonomous sensor networks, where the aim is to deploy micro-sensors and associated electronics in the environment. These sensors are placed in a network and must be able to communicate with each other: they can be used in a wide range of fields, from healthcare (implanted devices), intelligent buildings (structural monitoring), radio identification (RFID tags), automotive or even predictive maintenance (for machines and infrastructures). At present, the lifespan of these sensor networks is limited by that of the batteries used to power them, which poses a problem in applications requiring a permanent network involving a large number of sensors. Network maintenance then becomes economically and logistically impractical. Indeed, despite continuous improvements in microbattery capacity and reductions in the power consumption of electronic components, on-board energy runs out either because it has been consumed, or through self-discharge, after a few years at best.

The question of energy is therefore central to these networks. One pertinent solution is to recover the energy available in the sensors' environment (vibrations, heat, light) to power them. This would significantly extend battery life, or even eliminate it altogether. However, as the surrounding energy is recovered intermittently, an electrical energy storage device is still required to ensure the energy autonomy of each network element.

Despite their lower energy density than batteries, supercapacitors (or electrochemical capacitors) are very attractive in this respect, as they have an almost unlimited lifetime. Supercapacitors that can be integrated at system or chip level as miniaturized components would therefore enable major advances in the development of embedded and energy-independent systems. This alternative to microbatteries is currently driving the development of microsupercapacitors.

Although microsupercapacitors have been the subject of an increasing amount of research since 2006, they have yet to find any concrete applications. In fact, their low surface energy density means that they cannot be used to power sensors or any other electronic component on a long-term basis. To increase their energy performance with a limited surface footprint in the electronic circuit, the microsupercapacitor electrode must contain a significant amount of active material per...