Measuring the surface pressure of a lithium ion battery can provide useful diagnostic information besides the three traditional measurable signals: current, voltage and temperature. The surface pressure change can be caused by the volume expansion of the electrode material which is a reversible process, or gas evolution inside the battery which is an irreversible process. In this work, two types of sensors were used to measure the battery surface pressure change. Load cells were used in a special designed cell holder to measure the surface pressure change of a commercial lithium ion pouch cell cycled at different C-rates. The pouch cell was applied with 0.1 MPa pressure to emulate the environment in a battery pack. When the battery state of charge changes between 0 % and 100 %, the surface pressure of the battery changes between 0.1 MPa and 0.16 MPa and this is independent of the C-rate. However, at a lower C-rate (C/5 or lower), the surface pressure change shows a clear staging behavior which can be related with the phase change in the electrode material. In addition, pressure film sensors were used to measure the surface pressure of prismatic large-format NMC622 cells during various load profiles, including dynamic load cycles relevant for heavy-duty electric vehicles. The results indicate a surprisingly good correlation of pressure vs. state of charge, and also very early indications of ageing.
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