Making Batteries Last Longer A low-cost practical diagnosis technique for lithium-ion batteries Yu Merla1, Billy Wu2, Vladimir Yufit3, Ricardo F. Martinez-Botas1, Nigel Brandon3, Gregory Offer1,3

1 Department of Mechanical Engineering, Imperial College London 2 Dyson School of Design Engineering, Imperial Collage London 3 Department of Earth Science and Engineering, Imperial College London

[1] Novel application of differential thermal voltammetry as an in-depth state of health diagnosis method for lithium-ion batteries, Y. Merla, B. Wu, V. Yufit, R.F.

Martinez-botas, N.P. Brandon, G.J. Offer, J. Power Sources. 307 (2016) 308–319. doi:10.1016/j.jpowsour.2015.12.122.

[2] Differential thermal voltammetry for tracking of degradation in lithium-ion batteries, B. Wu, V. Yufit, Y. Merla, R.F. Martinez-botas, N.P. Brandon, G.J. Offer, J.

Power Sources. 273 (2015) 495–501. doi:10.1016/j.jpowsour.2014.09.127.

1. Differential Thermal Voltammetry (DTV) • Novel in-situ diagnosis technique for tracking degradation in lithium-ion batteries • Only required voltage and surface temperature measurement • Carried out by observing entropic heat changes during a galvanostatic charge or discharge • Its simple computation can be handled by existing battery management systems • Low cost hardware and software requirements makes DTV a practical for applications such as electric

vehicles and smartphones. • dT/dV plotted against potential to give indication on changes in electrode stoichiometry • Each dT/dV peak represents a combination of different contributions from positive and negative

electrode phases

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2. Accelerated aging experiment

3. Diagnosis method comparison

4. DTV peak analysis

Cell Load Temperature

1 Held at 4.2V 55 ºC

2 1C cycling 55 ºC

• Commercial 5Ah lithium-ion cells • Carbon negative electrode • Nickel manganese cobalt oxide

positive electrode

DTV gives information as good as slow-rate cyclic voltammetry (SRCV) and incremental capacity method (ICM)

Additional information on the entropy characteristics Results automatically take into account changes in temperature. Can be carried out during a 1C – 3C charge or discharge Standard thermocouple to measure surface temperature

Evolution of decoupled DTV peaks used to track electrode stoichiometry Changes in peak parameters identify stoichiometric drift in cell 1 No significant stoichiometric drift is observed for cell 2 despite similar capacity loss Such findings can be used for adaptive control of cell operation to optimise cell

lifetime and available energy

Battery pack diagnosis using DTV Positional diagnosis using DTV

with thermal imaging camera