High-power 18650 Li-ion cells have been developed for hybrid electric vehicle applications as part of the DOE Advanced Technology Development (ATD) program. The thermal abuse response of two advanced chemistries (Gen1 and Gen2) were measured and compared with commercial Sony 18650 cells. Gen1 cells consisted of an MCMB graphite based anode and a LiNi0.85Co0.15O2 cathode material while the Gen2 cells consisted of a MAG10 anode graphite and a LiNi0.80Co0.15 Al0.05O2 cathode. Accelerating rate calorimetry (ARC) and differential scanning calorimetry (DSC) were used to measure the thermal response and properties of the cells and cell materials up to 400°C. The MCMB graphite was found to result in increased thermal stability of the cells due to more effective solid electrolyte interface (SEI) formation. The Al stabilized cathodes were seen to have higher peak reaction temperatures that also gave improved cell thermal response. The effects of accelerated aging on cell properties were also determined. Aging resulted in improved cell thermal stability with the anodes showing a rapid reduction in exothermic reactions while the cathodes only showed reduced reactions after more extended aging.