Researchers find that building a better battery is like baking a cake ‹ all you need is the right ingredients
By Chris Burroughs
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READY FOR BAKING -- Tim Boyle (1846) checks a flask that contains the dried cathode precursor powder. The powder will then be put into a furnace and baked into the desired cathode material for the lithium ion battery. (Photo by Randy Montoya)
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For inorganic chemist Tim Boyle and chemical engineer Jim Voigt, both in Materials Processing Dept. 1846, building a better lithium ion battery is much like baking a cake -- a matter of putting together the right ingredients in the cathode. "We've tried various combinations of lithium [a light weight metal] with manganese, cobalt, nickel, chromium, and aluminum and are making some breakthroughs," Tim says.
If the right combination of materials can be found, lithium ion rechargeable batteries may become economical enough and have a long enough run time to be practical to power electric cars or replace existing traditional lead-acid batteries.
Dan Doughty, Manager of Lithium Battery R&D Dept. 1521, says Sandia's efforts to improve the lithium battery have been a team effort "all the way."
"We have people in 1800 doing synthesis of the materials, 6100 who do computer modeling, and 1500 who do battery materials testing and electrochemistry," he says. "I have been very pleased with the progress of this interdisciplinary team. It is an example of the synergy that characterizes a national lab -- and specifically Sandia -- environment."
A battery consists of three basic parts -- two electrodes (a cathode and anode) separated by an electrolyte. Lithium ion batteries use host materials for the electrodes (for example, carbon as the anode and lithium cobalt oxide as the cathode) to avoid using metallic lithium, thereby improving safety. Electrochemical reactions at the electrodes produce an electric current that powers an external circuit. During charge and discharge of lithium ion rechargeable batteries, lithium ions are shuttled between the cathode and anode host materials in a "rocking horse" fashion.
Sandia has done extensive past work in the area of improving carbons for use as anodes. The cathode work builds on the previous anode endeavors, Dan says.
Lithium ion batteries are commonly found in laptop computers and camcorders. Their use, however, is limited to small electronic devices because of their cost and safety concerns. Several materials contribute to the high cost, but the most frequently used cathode material -- lithium cobalt oxide -- is extremely expensive.
Two factors drive the quest for a better lithium ion rechargeable battery, Tim says. First, the batteries are more "environmentally friendly."
"Lithium magnate is like sand. It has almost no environmental impact -- unlike lead acid batteries that contain poisonous heavy metals." Tim says. "Also, the lithium battery can be recharged -- meaning that it isn't thrown out, but used over and over again." The second reason is that lithium batteries are light-weight and provide more electricity than non-lithium batteries of equal size and weight. As a result, they are ideal to power portable electronics, a rapidly growing market. Also, if perfected, they might be used in electric cars, which require batteries that are cheap, light, powerful, and long-lasting.
The challenge, then, is to find the right combination of cathode elements.
Tim and Jim are in a unique position to do this because of a process they invented and patented three years ago to combine elements. "We can make the materials here that others can't because we have this system in place," Tim says.
Their patented system is a simple waterless process in which the materials being combined are dissolved in methanol. The solution is then dried in a vacuum, baked at 200 degrees C in a box furnace for 24 hours, transferred to a tube furnace where it is heated to 800 degrees C, and held for 24 hours under a flowing oxygen atmosphere. The result is a homogenous powder where the elements are not separated.
Tim says two University of New Mexico student interns, Cory Tafoya and Sara Vick, have been his "hands" and are responsible for a lion's share of the technical work. They generate the various mixtures and process them into the cathode material.
Mark Rodriguez of Materials Characterization Dept. 1822 uses X-ray diffraction to prove these materials are phase pure. Mark also is studying the various structural changes these materials undergo by using a "transparent" battery in his X-ray instrument.
Deciding which elements to combine is not a "hit or miss" testing process, Tim says. Before elements are combined, a team lead by Randy Cygan and Hank Westrich, both of Geochemistry Dept. 6118, develop computer models of what the structural integrity of the final material will be. After determining via the computer modeling which combinations are best, the solutions are mixed, powders processed, and batteries tested.
Testing of the new materials' performance is done by Dave Ingersoll and Jill Langendorf, both of Lithium Battery R&D Dept. 1521. They measure capacity and useful life of the new cathode materials using electrochemical methods.
Tim's experiments show that cobalt, nickel, manganese, and other transition metals might be the most effective combination of materials. The introduction of the nickel to replace some of the cobalt would reduce the cost of the final material while maintaining the high capacity. The manganese allows for more flexibility in the charge distribution and also would reduce cost of the product because it is replacing the expensive cobalt. Another advantage of using manganese is that it is considered a benign material and therefore environmentally less damaging than the other elements.
Sandia has long been a leader in designing and building batteries for defense applications. The lithium battery cathode development program is funded by a DOE Office of Basic Energy Sciences initiative to develop novel, high-performance battery materials.
"They want us to find a higher capacity material for the cathode that will give these batteries a longer life," Dan says. "Tim and Jim's research fits right into this goal."
Last modified: December 07, 1998
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