Pushing the frontiers of lithium-ion batteries raises safety questions
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Energy Sector Analysis
The consequences of rare failures scale with the energy stored and put a premium on designing for safety.
Pushing the frontiers of lithium-ion batteries raises safety questions By Arthur L. Robinson Feature Editor M. Stanley Whittingham
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t Underwriters Laboratories, where researchers develop standards and testing procedures for batteries, J. Thomas Chapin, vice president of research, sees a surge in the production of lithium-ion batteries. Billions of lithium-ion cells are being manufactured monthly, a figure that will more than double with massive new facilities under construction or planned in the United States and Korea. “If failures occur in the wrong place, the consequences can be serious,” Chapin said, some as severe as the January 2013 incidents on Boeing 787 Dreamliners that grounded the entire 787 fleet until a fix was in hand. The recent publicity about hoverboard fires further raises the public impression that lithium-ion batteries are not as safe as they could be, despite their impressively low failure rate. Lithium-ion batteries with their high energy density, long lifetime, and comparatively affordable cost have been driving a portable electrical power revolution in consumer electronics, industrial equipment, and medical instrumentation. But packing a lot of energy into a small volume is also what makes them dangerous if they are not treated with respect, said Mike Wentz, who oversees the transportation of dangerous goods for American Airlines, which, along with other airlines, will only carry lithiumion batteries that have been properly declared by the shipper. The trend toward larger batteries presents new safety issues, added Christopher Orendorff, manager of Power Sources R&D at Sandia National Laboratories. “New failure modes become evident in large-scale batteries, and it is critically important to find robust materials and to engineer safety into the batteries,” he said. Depending on the current and voltage required, a rechargeable battery may comprise a single cell or up to many thousands of cells. The prototypical lithium-ion battery cell starts with a lithium–cobalt–oxygen cathode (LiCoO2), which has a layered structure in which lithium ions lie between the cobalt–oxygen planes. Similarly, the anode is graphite, another layered material, with lithium again intercalated between graphene planes. For high lithium-ion mobility, electrode wettability, and electrochemical compatibility with the electrodes and performance requirements, the electrolyte is a non- aqueous liquid mixture of organic solvents and salts, such as alkyl carbonates and LiPF6. To electrically isolate the electrodes from each other but allow the lithium ions
M. Stanley Whittingham, Binghamton University, The State University of New York, USA Arthur L. Robinson, [email protected]
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MRS BULLETIN
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VOLUME 41 • MARCH 2016
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www.mrs.org/bulletin • Energy Quarterly
to pass through, there is a 50-μm-thick porous separator sheet made of a polyolefin, such as polyethylene. There is no single sol
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