Extract from this site:- http://www.allaboutsymbian.com/features/item/15775_How_do_Lithium_batteries_work.php
"Is Lithium Polymer different?
The chances are that if you read this site, you've heard of Lithium Polymer (Li-Polymer) as a distinct battery type from Li-Ion batteries. The difference between them lies in the material used as the separator. Rather than an inert substance with holes covered in electrolyte, the separator is made of a micro-porous polymer covered in an electrolytic gel that also serves as a catalyst that reduces the energy barrier in the chemical reaction between cathode and anode. Therefore, Li-Polymer batteries allow for a slight increase in energy density. However, this advantage is offset by a 10% to 30% cost increase. Therefore, because the same materials are used for cathode and anode, Li-Polymer batteries follow the same chemical process as Li-Ion batteries and so are not a distinct class.
Because the solid polymer is flexible, it is possible to construct flexible batteries and batteries that can be easily formed into various shapes and sizes, even thin films. So you'll most often see Li-Poly used for batteries which are relatively thin (e.g. Nokia's 'hero' BP-4L battery used in a dozen devices) or oddly shaped (e.g. to fit round other components in a tightly packed phone).
Just as with Li-Ion batteries though, Li-Polymer batteries are slowly degrading from the day they are created, and are subject to the same harm caused by deep-discharges."