Electric vehicle technology may be bad news for mechanical engineers. But for the chemists researching new materials to put into electric batteries to make them light, powerful and affordable, the trend towards more electric vehicles is good news.
Researchers at the Massachusetts Institute of Technology have made a breakthrough with the development of a new material for a rechargeable lithium-ion battery.
They are using computer techniques to analyse key chemicals in the battery to see whether better materials could be used.
Their surprise findings overturn present theory and practice and should make it possible to develop low-cost Li-ion batteries.
Li-ion batteries pack the most power into the smallest space and so they would be an ideal choice for an electric vehicle. But, to date, their high cost limits their use to small appliances such as mobile phones and laptop computers.
Cobalt is the main problem. As lithium cobalt oxide, the material forms the cathode or negative pole of the battery. But cobalt is extremely expensive.
Three MIT professors Yet-Ming Chiang, Gerbrand Ceder and Donald Sadoway have found that cobalt can be replaced by aluminium, which is cheap and light.
Further, they found that aluminium, in the form of lithium aluminium oxide, has the potential to generate a high cell voltage which would result in a more powerful battery.
But they also found one serious drawback. Pure lithium aluminium oxide compound does not give up electrons easily (if at all), making it a poor conductor and useless as the cathode in an electrical system.
To give the material conductivity Chiang, a ceramicist, suggested adding back a small amount of the cobalt compound, which has worked.
The next logical challenge was to make the new cathode material so that physical tests could be carried out to see if the computer predictions worked in practice.
Using Ceder’s computer modelling techniques, the group found that the aluminium and cobalt had to be incorporated at specific sites in the two-compound mix in order to get the predicted properties. Chiang and his student, again working with computer models, came up with physical samples each containing a different balance of aluminium and cobalt.
Sadoway, the chemist in charge of the project, has put the cathode material samples through their paces using existing Li-ion battery technology based on a conventional anode (positive pole) and a conventional electrolyte (which joins the two poles to form an electrical circuit).
The tests, according to Sadoway, worked ‘like a charm’. In fact, cathodes with the higher levels of aluminium produced such high voltages that electrolyte became unstable.
In the latest stage of the Li-ion battery research the team, working with MIT polymer physicist Professor Anne Mayes, has developed a new electrolyte made from plastics material rather than the usual liquid form.
The development opens up new possibilities since solids are much easier to contain than liquids. Incorporating battery packs into vehicle body panels is one possibility.
The final step is to develop a new anode material. But that is not a priority because existing materials have few limitations.
The ultimate vision is for a battery capable of powering a vehicle for 200 miles before recharge. Sadoway says solid state lithium battery technology provides the answer.
EVs wait in the wings, page 22