What’s the difference between a normal lithium-ion battery and a lithium polymer battery?

While both are members of the rechargeable lithium-ion family and operate on the same fundamental chemistry, the primary difference between a standard lithium-ion (Li-ion) battery and a lithium polymer (Li-po) battery lies in the electrolyte used to move ions between the electrodes.

Standard lithium-ion batteries use a liquid organic solvent as the electrolyte. Because the liquid must be securely contained to prevent leaks, these batteries require a rigid metal casing (usually cylindrical like a 18650 cell, or a hard rectangular pouch).

Lithium polymer batteries use a solid or gel-like polymer electrolyte. This allows the battery to be encased in a flexible, lightweight aluminum foil pouch rather than a heavy metal shell.