There are two kinds.
Lithium battery: The highest energy density, but be very careful, because the short circuit or overcharge and over discharge will cause damage to the battery, so it is generally necessary to bring a protective plate. Almost all of the early mobile phones used this type of battery, but because of the relatively heavy weight (formation restrictions) due to the use of a metal casing, the explosion was so powerful that it was gradually replaced by a lithium polymer battery.
Polymer lithium battery: Nowadays, almost all mobile phones use this kind of battery, which is characterized by thinness and lightness, and there are not many restrictions on the shape. The disadvantage is that there is no lithium ion in the cycle charging life. Also need to have a protective plate