The topic of exploding lithium-ion batteries has been debated to death in the wake of massive battery recalls over the last couple of years. Amidst the deft public relations maneuvering and finger-pointing, however, the question as to why they explode in the first place is still shrouded in mystery for many.
The most important thing to understand here is that lithium-ion technology is considerably more volatile compared to other forms of rechargeable battery technologies. Defects in the insulating membrane can result in a mini-explosion that rips a battery open to release steam in excess of 600 degrees Fahrenheit.
Manufacturers are aware that it is statistically probable for a lithium-ion to fail, though the calculations employed to sideline the risk are sometimes quite suspect. To determine the mean time between failures (MTBF), manufacturers take a sample of say, 1,000 batteries, which are then used until one fails.
Assuming that the battery that died did so after 100 hours, the MTBF for that batch is pegged at 100,000 hours, or 100 multiplied by 1,000. While satisfying to the QC manager, it is completely meaningless to the consumer. A MTBF of 100,000 hours implies that the battery will work for more than 10 years. This is false; because lithium-ion cells starts deteriorating the moment they are manufactured. On the shelf in a fairly hot warehouse, a fully charged lithium-ion battery could irreversibly lose up to a third of its maximum capacity in just one year.
This does not tell the full story however; until one realizes that lithium-ion itself is a constantly evolving technology.
The exact chemical composition in a modern lithium-ion cell will be quite different from the first commercial lithium-ion that Sony sold in 1991. This is because manufacturers are constantly working to squeeze the best performance by making variations in the battery chemistry.
In the on-going consumer electronics craze that saw an explosion of ever slimmer, high-drain gadgets, the envelope for performance is constantly pushed outwards. Insulating walls are made thinner for smaller batteries and new mixes of chemicals and surface coatings are put in to eke out that extra iota of battery life.
Problems can arise when -- as with manufactured products from time-to-time -- and enhancements don’t work the same way in the real world as they did in the lab. Also, problems might not even show up in the first generation, or until they are placed in high-drain gadgets that didn’t exist before, for example.
Another facade of the situation has to do with the fact that a rechargeable battery pack is actually made up of multiple battery cells. This is where you have manufacturers advertising “8-cell” or “4-cell” laptop batteries. What it also means is that raw lithium-ion cells are increasingly being shipped to another location for assembly into the final battery pack.
Because not all manufacturers are interested in making everything, many choose to buy lithium-ion cells from third parties to assemble into battery packs. Depending on cost efficiencies, it is possible to have battery cells that are made in Japan, but assembled in China or other lower-cost countries.
There are skeptics who believe that quality control – which is of paramount importance in this context, is less than desirable in China. This is exacerbated by the fact that a completed battery can no longer be inspected from the outside or easily tested. The argument is that workers can take shortcuts and substitute, say, an original insulator with cardboard. Another possibility, as companies such as Mattel experienced first-hand, is that counterfeit raw materials could creep into the bill of materials – with disastrous results.
Where it is arguable that there is little you can do as a single consumer, at least you can figure out where your battery pack is actually put together.