Lithium Ion (Li-1on)lLithium Polymer Batteries

The best prospects for future electric and hybrid electric vehicle battery technology probably come from lithium battery chemistries. Lithium is the lightest and most reactive of the metals, and its ionic structure means that it freely gives up one of its three electrons to produce an electric current. Several types of lithium chemistry batteries are being developed. The two most promising of these appear to be the lithium ion (Li-ion) type and a further enhancement of this, the lithium polymer type.

The Li-ion battery construction is similar to that of other batteries except for the lack of any rare earth metals that are a major environmental problem when disposal or recycling of the batteries becomes necessary. The battery discharges by the passage of electrons from the lithiated metal oxide to the carbonaceous anode by current flowing via the external electrical circuit. Li-ion represents a general principle, not a particular system. For example, lithium/aluminium /iron sulphide has been used for vehicle batteries. Li-ion batteries have a very linear discharge characteristic, and this facilitates monitoring the state of charge. The charge/discharge efficiency of Li-ion batteries is approximately 80%, which compares favorably with nickel-cadmium batteries (approximately 65%) but unfavourably with nickel-metal hydride batteries (approximately 90%). Although the materials used are non-toxic, a concern with the use of lithium is, of course, its flammability.

Lithium polymer batteries use a solid polymer electrolyte, and the battery can be constructed similar to a capacitor, by rolling up the anode. polymer electrode, composite cathode, current collector from the cathode, and insulator. This results in a large surface area for the electrodes (to give a high current density) and a low ohmic loss.