Toyota will introduce the cleanest and most-technically advanced Prius built to date at next month’s auto show in Frankfurt, Germany. A newly designed, compact lithium-ion battery enables the new plug-in Prius hybrid to achieve a remarkably low fuel consumption rating of 2.2 liters per 100 kilometers (107 miles per gallon U.S.) and CO2 emissions of just 49 grams per kilometer. It will go up to 20 km (or 13.4 miles) on battery power alone. The Prius plug-in hybrid will be on sale in the U.S. in early 2012 and in Europe next summer.