Topic 4: Battery Attribute and Safety Summary Tables
Another way to portray these different types of lithium batteries is by summarizing what seems to be known about the different chemical combinations with lithium. From a safety perspective, the “Thermal Runaway” characteristic noted below is of particular importance.
Sony, the maker of the lithium-ion cells in question, points out that on rare occasion microscopic metal particles may come into contact with other parts of the battery cell, leading to a short circuit within the cell.
Battery manufacturers strive to minimize the presence of such particles; however, complex assembly techniques make the elimination of all metallic dust a challenge. Cells with ultra-thin separators of 24µm or less (24-thousandth of an mm) are more susceptible to impurities than the older designs with lower Ah ratings. Whereas the 1,350mAh cell in the 18650 package could tolerate a nail penetration test, the high-density 3,400mAh can ignite when performing the same test. (See BU-306: What is the Function of the Separator?) New safety standards direct how batteries are used, and the UL1642 Underwriters Laboratories (UL) test no longer mandates nail penetration for safety acceptance of lithium-based batteries.