The 18650 cylinder is the most widely used lithium ion (Li-ion) cell geometry, powering everything from laptops to electric vehicles. Its capacity has been steadily increasing, and now more than ever, the safety of Li-ion batteries is of the utmost importance. Cell failure is extremely rare during normal operation, but under abusive conditions the active materials within Li-ion batteries break down exothermically, generating large amounts of heat that can lead to a positive feedback loop, fire and even explosions – a phenomenon known as thermal runaway.
High-energy density lithium ion batteries are used for a wide range of applications, from portable electronics and medical devices to aerospace and manned spaceflight. Maintaining a high standard of safety for lithium ion cells is more important now than ever before particularly since high-energy density cells are expected to operate under challenging conditions for applications that are often ‘mission critical’. For example, when a battery pack for the auxiliary power unit caught fire on a Boeing Dreamliner in 2014, the entire fleet of aircraft was grounded for several months due to passenger safety concerns1.
Finegan DP, Darcy E, Keyser M, Tjaden B, Heenan TMM, Jervis R, Bailey JJ, Vo NT, Magdysyuk OV, Drakopoulos M, Di Michiel M, Rack A, Hinds G, Brett DJL, Shearing P. Identifying the cause of rupture of Li-ion batteries during thermal runaway. Advanced Science 5, doi:10.1002/advs.201700369 (2017).
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