Lithium ion batteries
What are they?
Lithium ion batteries (often written Li ion batteries) are secondary (i.e., rechargeable) batteries in which lithium ions (Li+) shuttle between two electrodes via a lithium-conducting electrolyte. Lithium ions move from cathode (positive electrode) to anode (negative electrode) when charging, and from anode to cathode during discharge.
Why do we need them?
Lithium is the lightest known metal, and consequently lithium ion batteries are lighter and have higher capacities than other secondary batteries. In other words, they can be used to store more energy per unit weight, and are thus more efficient to transport. The need to reduce carbon dioxide emissions also means Li ion batteries will be increasingly used to take energy from its point of generation to its point of usage, particularly for renewable energy sources.
Where can they be used?
Small Li ion batteries made possible the portable electronics revolution, powering everything from mobile phones, watches and calculators to laptop computers and PDAs. Larger batteries are now being used in cordless power tools, such as drills, and electric bicycles. They are gradually replacing nickel hydride batteries in hybrid vehicles and other large-scale applications.
What are they made of?
Commercially, the most popular material for the anode is graphite. The cathode is generally one of three materials:
- A layered oxide, such as lithium cobalt oxide;
- A polyanion-based material, such as lithium iron phosphate; or
- A spinel, such as lithium manganese oxide.
The electrolyte is usually a liquid, but gel and polymer types are also under development. A new type of Li ion battery, the Li-air cell, uses lithium metal as the anode, and oxygen (from air) as the cathode.
Research by the Consortium includes development of lithium iron phosphate cathodes and lithium-air cells. The latter in particular promises the highest capacity of any Li ion battery, while the former should enable large-scale batteries to be developed for automative (hybrid) and other demanding applications on account of its high stability.
The 
