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5.5.1 Definition

Batteries and supercapacitors are devices that store electrical energy.

Battery stores electrical energy in chemical form and thus converts chemical energy into electrical one. It stores a large amount of energy and releases it slowly. When this conversion is a reversible process, the battery is rechargeable. Non rechargeable batteries are not considered here.

A capacitor, a passive electrical component, stores energy in the electric field between a pair of conductors. It stores a small amount of energy but releases it quickly.

A supercapacitor is a capacitor that stores a larger amount of energy and releases it more slowly than a simple capacitor.

This can be sum-up in the following Ragone diagram[i].

Distribution of capacitors, supercapacitors, batteries and fuel cells in terms of specific energy and power

Different kinds of batteries are developed. Classical batteries for transport or static electric storage are still of great interest, and the main expected progress concern their storage capacity, the life time, the weight, the use of materials available and environment-friendly aspects. This topic is of great interest for automotive since hybrid and electric cars are under development.

Due to the developments of renewable and alternative energy sources, like photovoltaic systems, new storage solutions are also required. Batteries adapted to these specific energy production means and management are under development.

One of the greatest challenges for storage systems development is mobility. The exponential use of portable devices results in an increase of the amount of functions and of energy consumption. That is what drives R&D activity on miniaturised batteries. The main criteria for these systems are: autonomy, size, safety, charging time and cost.

Thanks to their ability to deliver high power in a limited time, supercapacitors are well adapted to applications for public transports, but also aerospace or wind turbine. In complement of systems providing constant energy, supercapacitors are able to quickly provide a peak of power when needed.

[i] A Case Study in Commercialising Nanotechnology: A. Kongats, Cap-XX - Nanotech Northern Europe 2008 - http://www.cap-xx.com/