Experimental and numerical investigation of heating power effect on thermal runaway propagation within large-format lithium iron phosphate battery

Thermal runaway propagation (TRP) inside lithium iron phosphate (LFP) batteries is an important part of TRP process of the module, but it has not been known clearly. This work experimentally and numerically investigated the overheat-induced thermal runaway (TR) characteristics of 243 Ah LFP battery and the influence mechanism of heating power on TRP within the battery. A series of TR experiments under 400, 700 and 1000 W heating power were conducted. The relationship between peak jet velocity and internal average TRP velocity (vTR) was revealed for the first time. Results show safety venting and TR time decreases with increasing heating power, while the internal TRP time prolongs. Batteries with faster internal TRP velocity tend to own higher peak jet velocity. The relationship between vTR and heating power is fitted as y = 0.2421e_x/466.8843 +0.2351 based on simulation result. vTR almost decreases linearly with heating power in the range of 200-1000 W, and then enters a plateau-like descending phase. In critical TR state, the width of TR region widens as heating power increases. The acceleration of vTR induced by low heating power is mainly attributed to a better pre-heating effect in nonTR region. This work can provide important guidance for the safety design of LIB batteries.