TAU Trends in Research June 1998

New TAU Battery Gives Cars a Boost

A new TAU battery, composed of thin films of lithium (anode) and pyrite (cathode) separated by a composite polymer electrolyte film, may help spur the development of a new generation of more efficient and economical electric cars.

Using a radical new design, in which thin films of lithium and pyrite are separated by a film of composite polymers, a team of TAU scientists headed by Prof. Emanuel Peled, and including Dr. Dina Golodnitsky and their colleagues, have developed rechargeable batteries, thinner than a razor-blade, which work well at temperatures not much hotter than a cup of coffee (90-1350C). Sheets of these batteries could be stacked or rolled (see figure above) so their combined voltage delivers quite a punch. For example, a 2 cm stack of 135 such thin batteries, each 0.15mm thick, could deliver high power at 200 volts.

The investigators' prototype studies with flat 1 cm2 batteries show that the thin (10-40 um) FeS2 cathode is reduced first to FeS(3) or Li2FeS2, and then to metallic iron. The theoretical energy density that can be stored by such a battery (based on 2.8 electrons per FeS2 molecule and an average voltage of 1.6 volts) is almost 810 watt-hours/kilogram, almost twice that of the best lithium ion batteries now available.

The TAU battery's materials are non-toxic, environmentally friendly and inexpensive. The thin-film design assures low cost, continuous process manufacturing and high power. The composite polymer electrolyte includes ultrafine LiI /Al2O3 powder and a polymer such as polyethylene oxide (PEO), none of which participate chemically in the battery's operation. The TAU team was the first to prove the rechargeability of pyrite cathodes in polymer electrolytes. Their most recent improvements, using a novel solid electrolyte and an extra-thin coated, 7um pyrite cathode, extends the useful lifetime of their batteries to over 500 charge-discharge cycles, with a storage capacity loss of less than 0.10% per cycle. The lithium-polymer interface was stable for over 10,000 hours (a year). Their battery also has useful overcharge and over-discharge protection mechanisms. On the basis of their data, the researchers expect that a practical electric car version with a specific energy of 170 watt hours/kilogram (four times that of a conventional lead acid car battery) should be feasible.

The cathode coating also reduces the charging rate to two hours (for batteries with a 10um thick cathode), instead of the 7-14 hours required by conventional batteries. The original small TAU prototypes have already been scaled up to 10 cm2, 40 millamps-hour size with no significant change in operating characteristics. Research and scaleup continue, with high expectations for matching both the performance, weight and cost goals set by the worldwide automobile industry.

For further information please contact:
Prof. Emanuel Peled
School of Chemistry
Raymond and Beverly Sackler Faculty of Exact Sciences
Tel Aviv University
P.O.B. 39040
Tel Aviv 69978
Israel

Tel.:	(00972) 3 / 640 8438
Fax.:	(00972) 3 / 640 9293 , 642 2649
E-Mail:	peled@post.tau.ac.il