ABSTRACT
This chapter examines the meaning and implications of applied voltage on a device by taking into consideration some important examples such as the capacitor, electrochemical cells in general, and the specific case of the battery. The authors focus on voltage viewed as a difference of Fermi levels at the contacts, in contrast to an electric potential difference. The final part is a summary of the principles of electrochemical batteries, with specific examples of practical battery cells and special emphasis on the operation and materials of lithium-ion cells. The contacts to a device allow us to change the applied voltage, inject or extract electric current, control carrier distributions, and govern different device properties, which are required to operate the device. Nanostructured energy devices usually operate by the combination of several materials. Groupings of different phases are arranged to funnel the charge carriers in a desired direction or provoke required chemical reactions.
