There is actually a difference between a lithium battery and a lithium polymer battery. Most of the batteries that you’ll encounter are actually lithium polymer or “LiPo” batteries. These batteries are encased in a pouch rather than a solid plastic casing. The electrochemistry of lithium ion and lithium polymer batteries is the same, it’s just the packaging that’s different. Actual LiPo batteries that have a non-liquid polymerized electrolyte (the stuff inside the battery) are not yet available to consumers. So basically lithium ion and LiPo batteries that you can buy today are the same in all but the packaging method.