Notes on Electrochemical Energy Storage meeting London 21 April

This one day meeting at the Institute of Engineering and Technology in London was staged jointly with the Royal Society of Chemistry. Here we report on two of the lectures which concerned devices that will increasingly interface with energy harvesting - rechargeable batteries and supercapacitors.

 

 

 

Dr Emma Kendrick of Fife Batteries, a materials research and development company specialising in high performance lithium-ion technologies, explained "Fundamental Battery Materials" describing the performance, safety and cost issues of the current lithium-ion technologies and examples of their use in electric vehicles. With the current lithium-ion chemistries there is a trade off between energy density, power and safety. This was illustrated with two examples of battery packs being developed for electric vehicles by Tesla and Lightning.

 

 

Tesla use a large pack of standard cylindrical cells with the lithium cobalt/graphite chemistry. This chemistry has relatively high specific energy densities, and although this chemistry is known to have safety problems, Tesla have engineered a comprehensive electronic and mechanical solution to this problem. The UK Lightning sports car possesses only a slightly inferior range of 188 miles and still stellar acceleration using an inherently safe, large format cell which contains the Li4Ti5O12 chemistry. Uniquely, it can charge in only ten minutes with a special charger - a huge marketing advantage over other electric cars which typically recharge overnight. The hand made Lightning was available from 2009. The Tesla recharges in 3.5 hours with a special battery - still inadequate for use during a journey.

 

Other chemistries emerging for use in EV applications include LiFePO4, from Valence and A123 amongst others, which is potentially rechargeable for up to 20,000 cycles - high for the industry, LiMn2O4 graphite/ hard carbon and those based on Li4Ti5O12 chemistry but "There is no ultimate solution yet". To progress she advocated new material research into nano materials and further cell development. "

 

 

Meanwhile we note that the world's best selling hybrid electric car, the Toyota Prius, will come out with a photovoltaic roof and plug in capability this year. It already employs electrodynamic regenerative braking, as do about 40 other electric cars currently on the market.

 

 

 

Professor Bob Slade of the University of Surrey then described the uses of supercapacitors. He noted that they have excellent fast charging and discharging but they can lose 40% of charge in 24 hours so they are only an adjunct to batteries. They compensate for the fact that batteries offer high specific energy or fast charge recharge but never both. There are many variants including asymmetric and symmetric electrochemical double layer capacitors and ones employing conducting polymers, composites or metal oxides. He is working on VO₂ nanorods, so far with indifferent characteristics. 100 micron films are of interest. He warned that supercapacitors currently suffer "initial capacitance fade" and some manufacturers naughtily quote capacity before fade. Temperature effects can be problematic, particularly with cars used for the equator to the arctic. In some applications the lack of capacitance at high frequency is an issue.

IDTechEx has just published a report on Batteries, Supercapacitors and Alternative Storage for Portable Devices 2009-2019 and is about to offer a newly researched report "EV Cars - Hybrid and Pure Electric Vehicles 2009-2019" which covers, inter alia, thermoelectric, photovoltaic and electrodynamic energy harvesting for cars. For more contact c.hindle@idtechex.com

 

 

 

 

For more attend: Energy Harvesting and Storage Europe 2009

 

Also read: Energy Harvesting and Storage for Electronic Devices 2009-2019