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Monitoring of lithium-ion batteries is of critical importance in electric vehicle applications in order to manage the operational condition of the cells. Measurements on a vehicle often involve current, voltage and temperature which enable in-situ diagnostic techniques. This paper presents a novel diagnostic technique, termed differential thermal voltammetry, which is capable of monitoring the state of the battery using voltage and temperature measurements in galvanostatic operating modes. This tracks battery degradation through phase transitions, and the resulting entropic heat, occurring in the electrodes. Experiments to monitor battery degradation using the new technique are compared with a pseudo-2D cell model. Results show that the differential thermal voltammetry technique provides information comparable to that of slow rate cyclic voltammetry at shorter timescale and with load conditions easier to replicate in a vehicle.

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 Accelerated ageing of lithium-ion cells under various storage/loading conditions.  Degradation analysis was performed using various in-situ diagnosis methods.  Differential thermal voltammetry (DTV) suitable for electric vehicle application.  State-of-health estimation through quantitative analyses of DTV peak evolution. AUTHOR E-MAIL ADDRESSYu Merla -yu.merla09@imperial.ac.uk Billy Wu -billy.wu@imperial.ac.uk Vladimir Yufit -v.yufit@imperial.ac.uk Nigel P. Brandon -n.brandon@imperial.ac.uk Ricardo F. Martinez-Botas -r.botas@imperial.ac.uk Gregory J. Offer -gregory.offer@imperial.ac.uk ABSTRACT Understanding and tracking battery degradation mechanisms and adapting its operation have become a necessity in order to enhance battery durability. A novel use of differential thermal voltammetry (DTV) is presented as an in-situ state-of-health (SOH) estimator for lithium-ion batteries.Accelerated ageing experiments were carried on 5Ah commercial lithium-ion polymer cells operated and stored at different temperature and loading conditions. The cells were analysed regularly with various existing in-situ diagnosis methods and the novel DTV technique to determine their SOH. The diagnosis results were used collectively to elaborate the degradation mechanisms inside the cells. The DTV spectra were decoupled into individual peaks, which each represent particular phases in the negative and positive electrode combined. The peak parameters were used to quantitatively analyse the battery SOH. 2A different cell of the same chemistry with unknown degradation history was then analysed to explore how the cell degraded. The DTV technique was able to diagnose the cell degradation without relying on supporting results from other methods nor previous cycling data. KEYWORDS:

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