Dear Colleagues

Probably one of the most fascinating but critical improvements urgently needed for the new generation of electrically-based devices (from mobile phones to electric cars) with lower emissions is improved battery technology. Certainly there have been enormous amounts of money invested in finding better battery technology but the road has been rather rocky.

There have been attempts at other innovative storage technologies such as fly wheels. However, these are tricky to develop because of the need for high quality materials, a reliable vacuum and size is directly related to energy capacity.

A fundamental problem is that for both the internal combustion engine and batteries the energy is stored in their chemistry. However, internal combustion engines do not need to store the heaviest component (oxygen) and thus have a virtually unassailable advantage. Similarly with safety – batteries have all the components for a fire in the one box; whereas internal combustion engines need oxygen externally to burn. Petrol stores sixty times more joules per kg than a lithium ion battery.

As most of you know – batteries have three key components: an anode, cathode (referred to as electrodes) and the electrolyte that allows the positively charged ions to move from one electrode to the other. Currently the most successful battery is the lithium-ion one. These power many of the electric and hybrid vehicles hitting the roads. However, they have the awkward propensity to overheat and create fires (such as on the recently grounded fleet of Boeing’s 787 Dreamliners).

A possible leading technology is that of the lithium air battery – using atmospheric oxygen as the electrolyte. However, these are still very unreliable and highly flammable so considerable effort has to go into protective safety systems to minimise any fire. Another interesting strategy is to move beyond lithium (one valence electron) to multivalent ions such as magnesium (two valence electrons) and aluminium (three valence electrons). However, this is likely to be offset by the fact that a magnesium atom weighs 3.5 times that of a lithium atom for only twice as many electrons (aluminium has a slightly lower opportunity cost). Note that NiMH batteries have been available for the past thirty years, with 100Wh/kg. Lithium Ion batteries achieve 150Wh/kg at best. Lead-acid batteries have been close to 30Wh/kg; whereas Nickel Cadmium averages 40-60Wh/kg.

Another interesting strategy is the use of so-called flow batteries. In a conventional battery, the battery’s charge is held as chemical potential energy in the two electrodes of the battery. In a flow battery, the charge is held in the vastly greater electrolyte – thus allowing these types of batteries to be made huge in size with large amounts of energy.

Thanks to The Economist and their rather volatile (but generally knowledgeable) discussion forum for some interesting ideas on batteries.

Perhaps in looking for inspiration for new technologies we should heed the advice of William Bridges: Genuine beginnings begin within us, even when they are brought to our attention by external opportunities.

Yours in engineering learning


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