Rechargeable batteries that are
light and small facilitate the fast growth of the markets for mobile phones,
laptop computers and other portable equipment. Lithium ion batteries have the
highest gravimetrical and volumetrical energy density and show considerable
promise for further improvements. The essential ingredients of any battery are
an anode and a cathode that are separated by an electrolyte. In each of these
components various physical processes take place that enable the functioning
of the device, and a flavour of these processes will be given here.
During (dis-)charge a battery should have a constant output potential; this is realised by continuously having Li-rich and Li-poor phases next to each other in equilibrium in the electrodes. Using NMR experiments we were able to show how ion transport takes care of the establishment of such solid state equilibria on 100 nm length scales and ms timescales. The electronic and ionic charge transports are closely connected as can be observed from the absence of ionic mobility below a temperature where electronic charge ordering takes place in a manganese oxide cathode. Last but not least it will be discussed how a polymer and ions interact in a polymer electrolyte.