TU Professor's Work on Battery of Future Jolts Industry
Thursday, September 02, 1999
University of Tulsa chemistry professor Dale Teeters, who is working on creating a lithium-polymer battery – thin as a credit card but packing more power than conventional batteries – has attracted the attention of Hydro-Québec, one of the world’s largest electricity companies, which is collaborating with industrial giant 3M to develop a lithium battery.
Hydro-Québec has invited Teeters to Canada in September to discuss his latest findings, which may overcome a major hurdle in developing these batteries of the future.
His research is so promising that he recently garnered more than $450,000 in funding: a grant of $315,000 from the Department of Defense, and matching funds of $144,000 from the Oklahoma State Regents for Higher Education. These funds were obtained through Oklahoma’s Experimental Program to Stimulate Competitive Research (EPSCoR).
Lithium batteries could be used in cell phones, laptop computers and in cars and space craft where space is at a premium. While a standard 12-volt, lead-acid car battery produces two volts per each of its six cells, a lithium battery -- much smaller and lighter -- can generate more than 3.5 volts per cell.
However, Teeters explains, the advantage of lithium, a metal, is also its downfall. It is very reactive, which generates the desired high voltage, but lithium also causes corrosion, which impedes the flow of electricity.
Batteries have two electrodes that deliver the charge and an electrolyte through which charged ions move. In this case, the electrolyte is a polymer -- plastic. The lithium battery models used by Teeters for demonstrations look and feel like a credit card, but are transparent and have two shiny strips of metal (the electrodes) on one end. The lithium is laminated in a polymer sandwich to seal out the air and water that it reacts with. But corrosion has still been occuring where the lithium meets the polymer. The chemist’s term is “passivation.”
“Theoretically these batteries should have a very long life,” says Teeters. “But the passivating layer is what hurts the life expectancy the most.”
Teeters and his colleagues have determined what is happening chemically at that lithium-polymer interface, and they have devised a strategy for preventing the corrosion.
The TU group has placed individual molecules of polyethylene, a non-reactive plastic, on the polymer to form a very thin protective coating. “It still lets current through, but it also prevents lithium from corroding,” explains Teeters.
These accomplishments were presented at an international conference in June in Greece and will be published in Electrochimica Acta, the journal of the International Society of Electrochemistry.
“We have done some molecular-level engineering,” says Teeters. This work has been carried out with some special equipment -- unique to the region -- that allows his research team to “see” what is happening at the atomic level.
The TU researchers are using an atomic force microscope to observe and manipulate molecules. Teeters says the microscope senses the force exerted by the surface of a solid on the microscope’s tiny probe tip. This probe is so small that it can’t be seen with a regular light microscope. He compares the process to that of a needle on a record player that follows the grooves of a record. A laser is used to measure the changing topography.
“Most materials exert a mutual attraction when the distance between them approaches the atomic scale,” says Teeters. “The strength of the attraction depends on the distance between the surfaces.”
The probe, when scanned at a constant height across a surface, will sense an attractive force that rises and falls according to the topography. Data are transferred to a computer, which displays the shape of the scanned surface. For instance, an image of a layer of mica looks like the checkerboard pattern of a tweed coat. The “bumps” in the material are single atoms of oxygen.
In addition, the customized microscope also measures the current that passes between the probe and the sample being scanned. Says Teeters: “We can see the regions on the molecular level that conduct and those that don’t conduct.”
Films of polymer are kept for a few days in a liquid bearing the polyethylene molecules, which adhere to the film. The results -- the thickness and evenness of the polyethylene coating -- are checked with the microscope.
Both undergraduate and graduate students have been working on the project, including use of the microscope. While students hear about atoms and molecules in their classes, this is a unique opportunity to actually “see” them and to see how changing the structure of the surface changes the behavior of the substance.
Work is normally conducted in a vacuum or in glove boxes in an inert environment of argon gas. In addition, Teeters uses an impedance spectrometer to measure the electric properties of the material and to look at the interface between the lithium and the electrolyte material.
EPSCoR is a merit-based program started by the National Science Foundation to broaden the geographical distribution of federal funding of academic research and development.
Work on lithium batteries is also being conducted in this region at Eagle-Picher Technologies, LLC of Joplin, Mo., a leader in the manufacturing of special purpose batteries, and Advance Research Chemicals Inc. at the Port of Catoosa, which makes electrolyte materials.