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

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.