As I compose this, 50 of the coolest planes since the Concorde are grounded. The problem is not with the 787′s innovative carbon-fiber airframe or extra-large passenger windows, nor with its comfortable low-altitude pressurization or humidified air systems. It’s that a couple of lithium-ion battery packs have caught fire, just like those in some Sandy-flooded Fiskers and a crash-tested Volt.
Lithium-ion batteries are more susceptible to fire because they’re energy-dense, and the organic electrolyte they must use is flammable. A short circuit caused by a manufacturing defect or by flaws that develop in the ion-transfer membrane that separates the electrodes can cause a rapid buildup of heat and the potential for fire. Heat or fire in one cell can easily cascade through a battery pack, resulting in disaster — and grounded planes or bankrupt EV manufacturers.
Good news! A nano-technological cure is under development at my alma mater, the University of Illinois in Urbana-Champaign. Aerospace engineering professor Scott White, working in conjunction with Nancy R. Sottos (materials science and engineering) and Jeffrey S. Moore (chemistry), has proposed smearing a thin coating of nanospheres on either the anode or the separator layer to serve as a sub-microscopic fire brigade. At 2-40 nanometers in diameter, they don’t interfere with the movement of lithium-ions that produces current in the battery (capacity and energy density are unaffected), but they can perform useful tasks. Solid polyethylene and paraffin wax nanospheres melt in an overheating situation, coating the surface they’re applied to and effectively shutting down an overheating cell. Other materials can burst when a crack forms, releasing healing agents to keep the battery working. Different triggers like pH level, electric or magnetic fields, voltage, or pressure can release various agents, including fire retardants.
In early testing, the polyethylene spheres shut batteries down reliably at 230 degrees; the paraffin at 150. These temperatures are at least 45 degrees below the melting point of the materials used in the separator. On the down side, in early testing the spheres needed 6 seconds to shut the battery down, when a cell can go critical in more like a second. But Scott believes that further refinement of the materials will speed the process.
There’s no reversing a shutdown — once the spheres melt, that cell is rendered useless. But Scott’s team believes that shutting down a single malfunctioning cell can prevent the cascade effect that ruins an entire battery, so the rest of the battery pack can continue to function and the plane or car can complete its journey safely.
These materials are still in the research phase, so Professor Scott’s team will not be helping to put my beloved Dreamliner back in the air, but he sees no hurdles to manufacturing and applying the technology. His researchers are currently preparing for tests on larger-scale batteries. No formal talks have begun with manufacturers in the transportation sector, but “interest has been expressed.” It’s entirely conceivable that these nano-saviors can be worked into the 787s my preferred carrier Delta will begin receiving in 2020.
External link: http://blogs.motortrend.com/dream-lithium-ion-28557.html