ALBUQUERQUE, N.M. — Research underway at the US Department of Energy’s Sandia National Laboratories to improve lithium ion battery materials may result in smaller, longer-lasting batteries for applications as diverse as portable computers and electric vehicles.
The research combines a new mixture of metals to create the cathode portion of the lithium ion battery — a high-tech, environmentally friendly electrical energy storage device.
For inorganic chemist Tim Boyle and chemical engineer Jim Voigt, both in Sandia’s Materials Processing Department, 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 lightweight metal] with manganese, cobalt, nickel, chromium, and aluminum and are making some breakthroughs,” Boyle says.
If the right combination of materials can be found — and the researchers think they are close — 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.
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 to improve carbons for use as anodes. The cathode work builds on the previous anode endeavors, says Dan Doughty, manager of Sandia’s Lithium Battery R&D Department.
Current battery use limited
Lithium ion batteries are commonly found in laptop computers and camcorders. Their use, however, is currently limited to small electronic devices because of cost and safety concerns. Several materials contribute to the high cost, but the most frequently used cathode material — lithium cobalt oxide — is extremely expensive. This is where Boyle and Voigt’s research could make a difference. Two factors drive the quest for a better lithium ion rechargeable battery, Boyle says. First, the batteries are more “environmentally friendly.”
“Lithium manganate is like sand. It has almost no environmental impact — unlike lead acid batteries that contain poisonous heavy metal.” Boyle 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 lightweight 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, 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. Boyle and Voigt are in a unique position to do this because of a process they invented and patented three years ago to combine elements.
Patented Process
Their 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.
Deciding which elements to combine is not a “hit or miss” testing process, Boyle says. Before elements are combined, computer models are developed showing the structural integrity of the final material. After determining via the computer modeling which combinations are best, the solutions are mixed, powders processed and batteries tested.
The material’s performance is tested by measuring the capacity and useful life of the new cathode materials using electrochemical methods. Also, X-ray diffraction is used to prove these materials are phase pure.
Boyle’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 costs because it is replacing the expensive cobalt. Another advantage of using manganese is that it is a benign material and therefore environmentally less damaging than some of the other elements used in lithium batteries.
Sandia has long been a leader in designing and building batteries for defense applications. The lithium battery cathode development program is funded by a Department of Energy Office of Basic Energy Science 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,” Doughty says. “Boyle and Voigt’s research fits right into this goal.”
Sandia is a multiprogram DOE laboratory, operated by a subsidiary of Lockheed Martin Corp. With main facilities in Albuquerque, N.M., and Livermore, Calif., Sandia has major research and development responsibilities in national security, energy, and environmental technologies and economic competitiveness.
Technical contact:
Tim Boyle, tjboyle@sandia.gov, (505) 272-7625
Dan Doughty, dhdough@sandia.gov, (505) 845-8105