Experimental investigation of cascading failure in 18650 lithium ion cell arrays: Impact of cathode chemistry

This study provides a comparative analysis of dynamics and hazards associated with cascading failure in lithium ion cell arrays of different cathode chemistries. Each array consists of 3 x 4 cylindrical cells with lithium cobalt oxide (LCO), lithium nickel manganese cobalt oxide (NMC), or lithium iron phosphate (LFP) cathode. Each array is mounted in a wind tunnel supplied with a controlled gas flow. Thermal runaway is induced in one cell using an electric heater and then observed to propagate through the array. Experiments are conducted in nitrogen and air environments to study the combustion impact. Time-resolved recordings of cells' bottom surface temperatures are utilized to track the thermal runaway propagation and calculate a row-to-row propagation speed. The LFP cells are the only cells that do not always fully propagate thermal runaway. The speed of the propagation is found to be greater in air than in nitrogen. In nitrogen, all cells produce large amounts of hydrocarbons, CO and CO2, and minor amounts of O-2 and H-2. Total heats generated due to chemical reactions between cell components and flaming combustion of ejected materials normalized by the electrical energy stored are determined to be 3.5, 2.9, and 2.5 for LCO, NMC, and LFP cells, respectively.