Measurement of gas pressure inside large-format prismatic lithium-ion cells during operation and cycle aging

Abstract In this study we investigate the influence of the state of charge (SOC), temperature and aging on the gas pressure inside prismatic lithium-ion cells with a LiNi1/3Mn1/3Co1/3O2 cathode and a graphite anode. The internal gas pressure inside lithium-ion cells has so far been only investigated for small cells using large-size laboratory measurement equipment. We show for the first time that measuring the internal gas pressure is also possible for large-format prismatic cells and by using miniaturized pressure sensors that can be integrated into a battery pack. We also show that this measurement method enables the monitoring of the gas pressure during long-term cycling without leading to premature battery failure or accelerated aging. The gas pressure depends on the SOC in a non-linear way. This is caused by the dependence of the electrode volumes on the degree of lithiation. The gas pressure also correlates non-linearly with temperature, and the magnitude of temperature dependence increases with aging. During long-term cycling, the pressure irreversibly increases, which is most likely due mainly to gas formation. The increase in pressure correlates with a loss of capacity, which basically qualifies internal gas pressure for an indicator for state of health.