Manufacturing Li-ion batteries for safety and performance
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Energy Sector Analysis
The benefit of the Li-ion cell lies in its high energy and power density, which has given manufacturers scope to produce high-performance gadgets that are also very small. But this, in turn, can pose a problem.
Manufacturing Li-ion batteries for safety and performance By Angela Saini Feature Editor Micheal Austin
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n the spring of 2017, on a flight between Beijing and Melbourne, an unlucky passenger was left with burns to her face when the lithium (Li)-ion battery in her wireless headphones caught fire. Covered in the international press, the incident was the latest in a string of headlines about combusting gadgets blamed on failing batteries. Airlines are now banning suspect devices entirely, and Samsung was recently forced to recall millions of Galaxy Note 7 smartphones because of fears around overheating and fire. In 2016, half a million hoverboards were similarly recalled because of the risk of fire. Given the ubiquity of Li-ion batteries, manufacturers have naturally come under pressure to improve safety. When Li-ion batteries were introduced to consumers in the early 1990s, people were unprepared for such incidents. Although defect rates are extremely low (in September 2016, when Samsung recalled its Galaxy Note 7, it had registered 35 reports of battery problems, of 2.5 million phones in circulation), the problem appears more significant because of the hundreds of millions of Li-ion cells now in use around the world and the spectacular nature of their failure when it happens. Leaking alkaline batteries are problematic; even one exploding Li-ion battery is newsworthy. The benefit of the Li-ion cell lies in its high energy and power density, which has given manufacturers scope to produce high-performance gadgets that are also very small. But this, in turn, can pose a problem. If compromised, the separator between the cathode and anode can allow a short circuit and overheating. The electrolyte is not only highly flammable, but reaches such high temperatures when it combusts that it can cause even an aluminum casing to melt; this is a dangerous combination. A decomposing cell also produces vast amounts of oxygen. This creates the conditions for thermal runaway, potentially transforming a device into something short of a small explosive. Single cells may reach temperatures as high as 700°C during thermal runaway. “Any number of defects or outside variables can act as a trigger mechanism to start a fire,” said Said Al-Hallaj, adjunct professor in the Department of Chemical Engineering at the University of Illinois at Chicago. One common cause of failure is lithium deposition on the graphite anode when a cell is charged too quickly. Dendritic growth may then penetrate the separator, causing a short. Other causes of
failure include physical deformation of the battery, mechanical intrusion, and overheating. The demand to improve device performance, expand the variety of applications, and reduce the size of personal gadgets is placing further pressures on safety. “As cell companies race t
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