ANALYSIS AND QUANTIFICATION OF HAZARDS ASSOCIATED WITH CASCADING THERMAL RUNAWAY PROPAGATION IN LITHIUM ION BATTERY CELL ARRAYS
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Lithium ion batteries are among the most common and efficient electrical energy storage devices despite the thermal, fire, and chemical hazards they pose upon thermal failure due to abnormal conditions. The hazards are intensified when thermal failure propagates from a single cell to neighboring cells in a battery pack. A new wind tunnel experimental setup was designed and built to investigate the dynamics, gaseous emissions, and energetics of cascading failure propagation in 18650 form factor, 2600 mA h, lithium cobalt oxide cathode cell arrays. Ambient environment (N2 / air), cell state of charge (SOC; 50% / 100%), and cell arrangement (without 5 mm gaps between cell rows / with 5 mm gaps between cell rows) were all varied during tests to investigate different aspects of battery pack failure and quantify the impact of different failure mitigation strategies. On average, failure propagation speed was 7.5 times faster in air than in nitrogen, 8.5 times slower at 50% SOC than at 100% SOC, and three times slower with a 5 mm gap between cells than without it. All tested cell arrays ejected minor mass yields of O2 and H2, as well as comparatively large mass yields of total unburned hydrocarbons, CO and CO2. At 100% SOC, approximately 59 kJ of energy per cell was produced from the chemical reactions between cell components during failure. An additional 62.8 ± 18.4 kJ per cell was produced when the ejected battery materials during failure combusted in a reacting medium, but the combustion in the wind tunnel setup was highly incomplete due to the development of under-ventilated conditions. In a separate experimental setup with near complete combustion, combustion energy of 107 ± 17.7 kJ per cell was measured.