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The heart of most vehicles today, the internal combustion engine has advanced significantly over its century long history.
This series outlines some of the key innovations in engine technology before taking a look at alternatives to the combustion engine. This week, the lithium-ion battery.
Apart from fuel-cell vehicles, battery electric vehicles are another form of emissions-free, sustainable transport. Lithium-ion batteries are the key technology that has made battery electric vehicles vehicles an attractive alternative to combustion powered cars.
The idea and concept of the lithium-ion battery were developed by various scientists during the 1970s and the early 1980s. The first commercially produced lithium-ion battery was subsequently produced by Sony in 1991 for use in electronic devices such as laptop computers.
In the automotive sphere, Nissan’s 1997 Altra EV - sold in limited quantities in the U.S. - was the first commercially produced, fully electric vehicle that incorporated a lithium-ion battery.
The operation of a battery is dependent upon the same fundamental scientific principles as the fuel-cell; namely that opposite electrical charges attract. In this case, however, it is lithium-ions that move through the battery rather than hydrogen ions.
A lithium-ion battery consists of a positively charged anode, a negatively charged cathode and an electrolyte solution contained between these two electrodes. In a lithium-ion battery, the anode is made from a lithium compound such as lithium-cobalt oxide, and is the source of the lithium atoms. The cathode is usually made from a form of carbon such as graphite.
One of the key properties of a lithium-ion battery is that it is rechargeable. When the battery is being charged, lithium-ions from the anode travel through the electrolyte solution directly to the cathode. The electrolyte solution acts as a barrier for the lithium electrons, forcing them to reach the cathode via an outer circuit. The flow of these electrons through the outer circuit is electricity. In an automotive application, this outer circuit is connected to a motor that drives the car. Once both the lithium-ions and electrons reach the cathode, they recombine into lithium atoms and are subsequently stored by the graphite cathode.
When the battery is discharged during usage, the opposite occurs. The lithium-ions flow back to the anode whilst the lithium electrons flow through the outer circuit in the opposite direction.
Lithium-ion batteries aren’t the only type of rechargeable battery available, with NiMH (nickel-metal hydride) and NiCd (nickel-cadmium) batteries also used today.
However, for automotive use, lithium-ion batteries have a key advantage in terms of energy density. A lithium-ion battery can store more energy for its weight than other battery types. In turn, this means that the battery pack can be substantially smaller and lighter if lithium-ion technology is used, delivering significant side benefits such as improved performance and better ride and handling. Furthermore, lithium-ion batteries recharge more quickly than their NiMH and NiCd counterparts. Importantly, lithium-ion batteries do not suffer from the ‘memory effect’, where the battery loses its capacity if it is only partially discharged before being recharged.
Of course, these benefits all come with the main caveat that lithium-ion batteries are more expensive than their NiMH counterparts.
The benefits offered by lithium-ion batteries, together with the rapidly developing electric vehicle charging infrastructure and government incentives in the U.S. and numerous European countries, mean that battery electric vehicles are very likely to be the primary mode of sustainable transport in the foreseeable future.
Work on future battery technologies to succeed lithium-ion technology is already underway. One promising new technology is the solid state battery, where the liquid or gelatinous electrolyte in current batteries is replaced by a solid electrolyte. This technology has the potential to provide even higher energy densities and several other benefits for automotive applications.
What do you think of lithium-ion batteries? Are they the future of electric cars? Tell us what you think in the comments below.