Lithium ion batteries have been widely used as power source of 3C products, EV, HEV, PHEV and energy storage of green grid. However, as a solution to high energy density storage, lithium-ion batteries have been seriously plagued by the safety issues. In this Paper, the thermal runaway at full charged state and heat production of LiCoO₂/graphite battery during charge and discharge with different current density was investigated during every 500 cycles. Results showed that the heat production increased with cycles and the regularity of heat rate was deviated at the end of life cycling. The temperature of heat production decreased and the heat rate was accelerated as the cycle number increased during thermal runaway.