Differential Thermal Voltammetry As a Low Cost in-Situ Diagnosis Tool for Lithium-Ion Batteries

Abstract

Modern applications of batteries in portable electronics, electric vehicles and grid level energy storage, demands long lifetime in various operating conditions. Monitoring its state-of-health in real time and optimising its operation in a cost-effective manner presents a real challenge.Differential thermal voltammetry (DTV) is a novel in-situ diagnosis technique for tracking degradation in lithium-ion batteries based on relatively simple cell surface temperature measurements. DTV only requires temperature and voltage measurements and is carried out by measuring the change in cell surface temperature during a constant current charge or discharge. It is a complimentary method to the incremental capacity or slow rate cyclic voltammetry analysis as it has additional information on the entropy characteristics as a result of temperature measurements. Accelerated aging experiment was carried out on commercial lithium-ion cells where the cells were aged differently in a controlled environment. The cells were characterised regularly using the new technique. Each dT/dV peak in the resulting curve represents a combination of different contributions from positive and negative electrode phases (Figure 1). By decoupling these peaks and by monitoring the evolution of the peak parameters it is possible to quantitatively determine stoichiometric drift in the cell. Cell 1 which was stored at 55degC and held at 4.2V showed significant shift in electrode stoichiometry. On the other hand, cell 2 stored at 55degC and cycled at 1C showed little shift despite the similar capacity fade of approximately 10%. This novel application of DTV presents an opportunity to estimate the state of health of a lithium-ion battery through tracking of decoupled dT/dV peaks. These results can then feed in to adaptively control the cell operation based on the diagnosis to optimise cell lifetime and available energy. Its low software and hardware requirements make it a practical solution to existing and future systems. Figure 1. Decoupled dT/dV peaks for two aged cells at approximately 10% capacity fade. Cell 1 (left) was stored at 55degC and held at 4.2V. Cell 2 (right) was stored at 55degC and cycled at 1C. Schematics of combined phases are shown above each plot. Note the visible stoichiometric drift in cell 1.[1] Y. Merla, B. Wu, V. Yufit, R.F. Martinez-botas, N.P. Brandon, G.J. Offer, Novel application of differential thermal voltammetry as an in-depth state of health diagnosis method for lithium-ion batteries, J. Power Sources. 307 (2016) 308–319. doi:10.1016/j.jpowsour.2015.12.122.[2] B. Wu, V. Yufit, Y. Merla, R.F. Martinez-botas, N.P. Brandon, G.J. Offer, Differential thermal voltammetry for tracking of degradation in lithium-ion batteries, J. Power Sources. 273 (2015) 495–501. doi:10.1016/j.jpowsour.2014.09.127. Figure 1