Abstract
Management of battery systems is difficult due to the variety of physical processes that occur when a battery is put under an electrical load. These processes produce macroscopic side effects, such as stress/strain and temperature evolution, which originate at the electrode level. The electrochemical-thermal-mechanical phenomena in battery cells are highly coupled in applications such as electric vehicles. Because microscopic effects in battery electrodes can propagate into larger length scales such as the cell and pack levels, there are changes on the outside that can be observed.
Contact-free, non-destructive methods for measuring changes in battery temperature and strain could serve as tools to determine a battery's second-life prospects, and could also aid early fault detection. The lock-in thermography technique has been used to determine faults and locate defects within cells.1 It has also been shown that mechanical stresses can be used to monitor state of health (SOH) and state of charge (SOC).2,3 Laser scanning has also been implemented to generate strain distributions showing local mechanical effects during electrochemical cycling.4
A first step in understanding highly coupled systems is to characterize the individual phenomena in isolation. Figure 1 presents a contour plot that shows the result of a zero-displacement experiment, where the evolution of equilibrium stress within a constrained 3-cell battery pack is measured at various SOCs and at various ambient temperatures. This experiment has shown that thermally induced volume change can contribute as much to mechanical forces within a cell as intercalation/deintercalation stresses. In high-power applications such as electric vehicles, we expect to see consequences from both of these factors. So, we will be developing an experimental set-up that combines the techniques of lock-in thermography and laser scanning to simultaneously capture 2D strain and temperature distributions that arise in response to different current input signals. Data from the individual techniques, plus the combined experiment, can be used to see how a battery's response changes as a consequence of its thermal and mechanical state, and how the relative contributions of temperature and strain can affect battery operation.
References
Robinson, J. B. et al. Detection of Internal Defects in Lithium-Ion Batteries Using Lock-in Thermography. ECS Electrochem. Lett. 4, A106–A109 (2015).
Cannarella, J. & Arnold, C. B. State of health and charge measurements in lithium-ion batteries using mechanical stress. J. Power Sources 269, 7–14 (2014).
Mohtat, P., Lee, S., Siegel, J. B. & Stefanopoulou, A. G. Towards better estimability of electrode-specific state of health: Decoding the cell expansion. J. Power Sources 427, 101–111 (2019).
Rieger, B. et al. Multi-directional laser scanning as innovative method to detect local cell damage during fast charging of lithium-ion cells. J. Energy Storage 8, 1–5 (2016).
Figure 1