Electrical and Chemo‐Electrical Devices for Energy Storage

The pervasive use of mobile electrical devices such as laptop computers, mobile phones or GPS based
navigation devices have created an intensified need for efficient and compact ways of storing energy.
For these mobile and portable applications devices need to be optimized regarding size, weight and
power (SWaP).

Thinking in terms of electrical and electro‐chemical devices, we can discern non‐rechargeable
primary batteries (PB), rechargeable secondary batteries (SB) and fuel cells (FC). The former have a
specific capacity in terms of charge (Ampere hours, Ah) or energy (Watt hours, WH) and they also
have a charge density (Ah/kg) as well as a charge and discharge rate (higher or less than C) (SB,PB).
For all kinds of storage devices there are a number of parameters for optimization: Energy density
(energy per volume or weight, Wh/kg) and power density (power per volume or weight, W/kg).
Moreover, these storage devices offer different voltages depending on the material composition
which defines their electro‐chemical potential (SB,PB,FC). All of them are subject to a certain
temperature sensitivity and have their individual operating temperatures. In addition, fuel cells also
have a specific operating pressure.

Secondary batteries can additionally be characterized by their lifetime, denoted by their number of
charge/discharge cycles and their capacity degradation over these cycles.

Two more important factors in the use of storage devices are cost (€/Wh) and safety.

The best results in terms of energy density can currently be obtained via Lithium‐based batteries,
which nevertheless are dramatically inferior in this respect to fossil fuels. Lithium‐based batteries can
be combined with different materials that will optimize them wrt. single individual characteristics
such as power density or energy density but invariably at a penalty regarding the other
characteristics.

Finally, the performance of Lithium batteries can be variated using micro‐ or nano‐structured
electrodes (using nano technology).
Given all of these characteristics and constraints it is of high interest whether the recent advances in
battery technology could be put to use for aviation, be it for more electric aircraft or even all electric
aircraft. Given the energy and power densities, the weights and safety characteristics of modern
battery systems, will it be possible in the near future to have aircraft propelled solely by electric
power, even with serious restrictions on range and payload?

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