A cooperative research program on the thermal characterization and safety of lithium batteries is being carried out at IIT/Center for Electrochemical Science and Engineering and Tohoku University. This research includes experimental work for commercial lithium secondary batteries and performance prediction for scaled-up batteries. In this work, we present a set of thermal characterization experiments for lithium secondary battery cells under normal and abuse conditions. These show that the rise in cell temperature depends strongly on cell chemistry as well as discharge rate. Computer simulation of the cycling of scaled-up lithium batteries shows that the cell temperature profile also depends strongly on the surface cooling rate. An effective thermal management system is required to operate these batteries safely. This paper reviews the basic information needed for intrinsically safe design.