Electrical energy storage microdevices

The growing demand for energy for the next generation of miniaturized, portable electronic devices has led to a keen interest in exploring energy storage devices on a micrometric scale. Indeed, a huge number of Internet-connected devices will be deployed, each consuming very little energy, under equally low instantaneous power.

This article gives an overview of the state of the art of recent research into microdevices for electrical energy storage, in particular those involving electrochemical reaction mechanisms, and highlights their future importance for a wide spectrum of applications. A great deal of effort has also gone into the manufacture and integration of microsupercapacitors and all-solid-state microbatteries. These microdevices are characterized by a long service life and a wide operating temperature range. Compared with conventional solutions, the dense thin-film stack architecture reduces the diffusion length of ions, thus improving power density and favoring co-integration with miniaturized and heterogeneous systems. However, numerous challenges such as instability at interfaces, low energy density by volume and high manufacturing cost continue to hamper the wider diffusion of microbatteries and microsupercapacitors. Material selection, microtechnology implementation and performance indicators are analyzed. A Ragone diagram shows the trade-off between the power available at the terminals of the storage device and the energy stored. The impact of microdevice cycling is discussed. Finally, medium-term research directions, technical challenges and optimization prospects are also discussed.