Lithium-ion batteries are widely used for portable energy storage in space power and consumer electronics applications. While the performance of these batteries is mainly depended upon the electrochemical aspects and contact electrical resistance of the cell stack, issues relating to contact thermal resistance between various layers of the cell stack could become more relevant under high rate of charge/discharge and extreme temperature operating conditions. An experimental program was carried out to establish the contact thermal resistance of a typical cell stack comprising graphite-coated copper anode, lithium cobalt oxide-coated aluminum cathode, polyethylene/polypropylene separator and electrolyte under various contact pressures and temperatures. The cell stack was not electrically charged or discharged during present experiments. Tests were conducted over a range of temperatures from −20 to 50°C and pressures from 0 to 250psi (1.72MPa). The results show that, in general, resistance increases with decreasing pressure and the effect is significant when the pressure is reduced below 100psi. Damage to the separator due to hot spots was observed at interface temperatures greater than 80°C. Present results indicate that extreme operating temperatures may affect the performance of Li-ion batteries.