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The introduction of lithium-ion batteries in the early 1990s gave a huge boost to the development of portable computers because they packed more energy into a smaller, lighter package than their predecessors – nickel cadmium and nickel metal hydride cells.
But the high energy density of lithium-ion may occasionally make the battery a combustion hazard if a fault develops. A short circuit can release the electric charge quickly enough to set fire to surrounding materials.
Although Dell and Sony have not released details of what they think went wrong, battery experts are reluctant to blame the lithium-ion cell on its own. The fault may lie in the way the Sony battery works with Dell’s recharging unit. The latest laptops are designed to charge much more quickly than their predecessors and, if the protection mechanism fails, they may overcharge.
If a fault leads to overheating, a lithium-ion battery can be a serious fire hazard because it contains inflammable organic solvents such as ethylene carbonate. As the heat builds up, these may vaporise and rupture the battery wall. Then a fire can spread quickly to other plastic components within the computer.
Peter Bruce, a lithium-ion expert at St Andrews University in Scotland, said it was important not to exaggerate the risk. “The worldwide production of lithium-ion batteries exceeded 1bn last year,” he said. “The proportion of cells causing problems is statistically minute: 99.999 per cent function perfectly well.”
Prof Bruce added: “The problems are more related to quality control and reliability of manufacturing than to any intrinsic defect in lithium-ion technology.”