Investigating thermal runaway characteristics and trigger mechanism of the parallel lithium-ion battery

Thermal runaway is considered the main cause resulting in fire and explosions of energy systems containing lithium-ion batteries. This study presents a fundamental understanding of quantifying thermal runaway characteristics of the parallel battery and revealing the corresponding trigger mechanism by eliminating the thermal interactions between batteries. The influence of connection mode, number of batteries in parallel and connector thickness on thermal runaway triggering are concerned herein. The parallel connection can cause the thermal runaway to be triggered prematurely but has little influence on the thermal runaway characteristics. The transferred electricity between batteries is responsible for the premature trigger of thermal runaway in the parallel battery, whose value accounting for 4.6% of the battery capacity is sufficient to advance thermal runaway to the open time of the safety valve. Due to the joule heat resulting from the transfer of electricity, the local thermal runaway of the parallel battery occurs first in the upper zone near the electrode tabs, then propagates to the whole battery. Moreover, a mathematical model of the thermal runaway triggering in the battery in open circuit is proposed, and the dominant influence mechanisms of transferred electrical energy on the occurrence of thermal runaway in the parallel battery are developed.