Lithium-ion batteries have been in commercial use since the 1990s. Originally developed for use in consumer electronics, they are gaining popularity as a powerful, lightweight, and environmentally friendly alternative to lead-acid and other traction batteries.
All batteries consist of two electrodes (the anode and cathode), a separator to prevent the electrodes from touching each other and short circuiting, and an electrolyte that fills the remaining space in the battery. In traditional, lead-acid batteries, the electrodes are both made of lead and the electrolyte is a mixture of water and sulphuric acid. A chemical reaction between the lead and the sulphuric acid produces free electrons that flow out of the battery as electricity.
In lithium-ion batteries, the electrodes are made using lithium compounds: lithium-metal oxides for the cathode and lithium-carbon compounds for the anode. The electrolyte is a conductive medium, generally either a gel polymer or a liquid containing a lithium salt or an organic solvent. When generating power, the electrolyte enables lithium ions move from the anode to the cathode in a process known as intercalation. This produces free electrons, which leave the battery from the anode, move through the circuit as electricity and return to the cathode. The reverse happens during charging. The separator supports intercalation as it only allows lithium ions to pass through it. It prevents electrons and electrode particles from crossing the battery.
Generally, lithium-ion batteries are lighter and can be charged more rapidly than lead-acid batteries. As they have higher energy densities than traditional batteries, it is possible to make smaller batteries while retaining the same storage capacity. A key benefit of lithium-ion batteries is that as the chemical reaction taking place is reversible, there is no degradation of the electrodes over time. The batteries can therefore be charged many more times than their lead-acid battery equivalents. They are also more environmentally friendly as they do not contain any substances (such as lead or sulphuric acid) with a high environmental load.
On the other hand, lithium is a highly reactive substance, organic electrolytes are highly volatile and the anode often exhibits high thermal instability. As a result, li-ion batteries pose a fire risk if punctured or charged improperly. In particular, they can be subject to a dangerous process known as thermal runaway.