The Pelisse can be a confusing term because there were several forms over a 50 year period. The first form of pelisse worn from 1800 to 1810 was an empire line coat like garment to the hip or knee.
After 1810 it was worn full length and was a warmer longer sleeved coat than the Spencer, but often made of the same materials. A LOT OF INFORMATION !!!..look at http://www.fashion-era.com/Coats_history/pelisse_history_1.htm