Diagnostics methodology based on differential mechanical measurements for lithium-ion batteries

One of the main challenges in lithium-ion battery diagnostics is the absence of sensors directly measuring the health of the battery during operation. This parameter can be estimated from voltage and current measurements, employing differential voltage or incremental capacity analyses. However, this estimation is often challenging in real-world applications because the shape of the differential voltage and incremental capacity curves changes with increasing current rates, and some key features in the curves vanish, affecting the applicability of the method.

In this work, the potential of differential mechanical measurements (second derivative of expansion and incremental expansion) for battery diagnostics is revealed, explaining for the first time the correlation between mechanical and voltage responses of commercial active materials. A procedure for estimating stoichiometric limits and electrode capacities using differential measurements is proposed. This procedure is particularly suitable to assess battery degradation in real-world applications, requiring monitoring the variation of the electrode parameters at high current rates and without performing complete charge/discharge cycles.

Mechanical and voltage differential curves of LCO-graphite, LFP-graphite and NMC111-graphite batteries are performed and compared, showing a strong correspondence and highlighting the close correlation between mechanics and electrochemistry in lithium-ion batteries.

Consequently, this work demonstrates that mechanical differential curves can be used similarly to differential voltage and incremental capacity curves, but with the significant advantage that the key features of the curve do not vanish at higher current rates. This makes mechanical measurements a promising alternative tool for battery diagnostics, particularly in real-world scenarios.