As I understand it, the chemistry of Li-PO cells are the same as Li-Ion; in fact, the voltage is identical. The main difference is Li-PO has a flexible (polymer) housing wheras Li-Ion has a rigid (metal) housing. Li-PO cells can therefore be almost any size and shape, although most I've seen are still roughly rectangular. The polymer housing does mean however one must use more care when charging a Li-PO battery.
The individual cells are best charged using a "balancing" charger, which simultaneously charges the cells in a battery in parallel. While you can charge cells in series, and some chargers do it this way, it is not recommended since a single cell could overcharge which could lead to bad consequences (fire, explosions, etc.). BTW, some folks advocate using balancing chargers for LI-Ion batteries as well. It is further recommended that one not charge a Li-PO battery unattended. Model airplane users typically remove the battery from the airplane to charge it and some use a "charging bag" which is intended to contain any shrapnel etc.
I'm not sure how credible the doomsday scenarios are, but that's what I've read. (There's a member at "that other forum" who is a strong proponent of the doomsday stuff.
) I figure a Stainz boiler is at least as strong as any charging bag
and I use a balancing charger which I believe mitigates the hazards.
Anyway, I'm off to push the envelope (my own envelope, at least).
"It is one of the happiest characteristics
of this glorious country that official utterances are invariably
regarded as unanswerable."
-Sir Joseph Porter, First Lord of the Admiralty (HMS Pinafore)