The Li-Ion Battery Isn't Perfect, Either
Naturally, this technology has its own weaknesses, too, such as a natural aging process that applies to nearly every Li-Ion battery. This results in the overall diminution of battery capacity over time. In other words, the clock on a Li-Ion battery's life starts ticking as soon as the cells of which it is composed have been manufactured. But because battery packs are not labeled with their build dates, buyers can only hope that notebook vendors deliver only the freshest batteries inside their products. This also means that buying and storing spare or replacement batteries before they're needed is completely senseless.
The use of pure, highly active metallic lithium for the negative electrode in batteries has been discontinued since the mid-1980s for security reasons. In addition, it's important to use only the charger provided with a Li-Ion battery, and owners of such batteries should never succumb to the temptation to short the leads of such batteries. This could not only lead to thermal destruction of the battery itself, but also poses a considerable risk to life and limb. The electrolyte is composed of a lithium salt solution, and the negative electrode in a Li-Ion battery is made either of coke or pure graphite. The most common materials used for the positive electrodes in Li-Ion batteries nowadays include oxides of lithium and manganese (LiMn) or lithium and cobalt (LiCo). The use of lithium in such oxides also creates the side effect of noticeable heating should a battery be overcharged. In some pathological cases, lithium cobalt oxide electrodes can transform into pure metallic lithium during charging. Should this happen, the battery would heat up drastically; in a worst case scenario it could even burn up completely. To prevent this from happening, input power levels must be throttled during charging and battery temperature closely monitored throughout the charging process. Also none of the individual cells may be exposed to overly high voltage levels during the charging process. It's also important to ensure that voltage levels don't drop below some minimum threshold value during discharge, either. All of these things demand a built-in safety switch for such battery packs. The necessary cost for such a device has a definite and negative impact on the cost of Li-Ion batteries.