Battery calorimetry to enhance lifetime and safety of LIB

Summary:

With increasing energy density the safety and the thermal management of Li-ion batteries is becoming more and more important, because the thermal runaway can cause an ignition or even explosion of the battery with simultaneous release of toxic gases. In the last nine years we have established battery calorimetry as a powerful and versatile electrochemical-thermal characterization technique, which allows both advancements for the thermal management and the safety of batteries. With six adiabatic Accelerating Rate Calorimeters (ARC) of different sizes combined with cyclers the IAM-AWP now operates Europe’s largest battery calorimeter center, which enables the evaluation of thermodynamic, thermal and safety data on material, cell and pack level under quasiadiabatic and isoperibolic environments for both normal and abuse conditions (thermal, electrical, mechanical). It will be shown how sophisticated battery calorimetry allows finding new and quantitative correlations between different critical thermally and safety related parameters that will help to design safer systems.

Calorimetry allows the collection of quantitative data required for optimum battery performance and safety. This information is needed to define the requirements for cooling and thermal management and adapt them accordingly. The calorimeters can be used for studies on heat generation and dissipation of Li-ion cells and are coupled to a battery cycler in order to perform the measurements during charging and discharging of the cells under defined thermal conditions, which are quasiadiabatic or isoperibolic. The cycle life can be studied by performing calendaric and cyclic ageing tests and characterising the cells at fixed time intervals concerning changes in heat generation and temperature profile, which serves as a “fingerprint” for the state-of-health (SOH).

For the advanced Li-ion technology, a holistic safety assessment is in the focus, because the thermal runaway can have multiple interacting causes and effects. A test in the calorimeter reveals the entire process of the thermal runaway with the different stages of exothermic reactions. It will be presented how battery calorimeters allow to perform safety tests on cell and pack level by applying thermal [1, 2], mechanical or electrical [3] abuse conditions. As a result of the different tests quantitative and system relevant data for temperature, heat and pressure development of materials and cells are provided. In addition it will be explained how calorimeters allow studying the thermal runaway propagation in order to develop and qualify suitable countermeasures, such as heat protection barriers, which is currently becoming a very hot topic.

References:
[1] C. Ziebert et al., in: L.M. Rodriguez, N. Omar, eds., EMERGING NANOTECH-NOLOGIES IN RECHARGABLE ENERGY STORAGE SYSTEMS, Elsevier Inc., ISBN 978032342977, 195-229. 2017.
[2] B. Lei, W. Zhao, C. Ziebert, et al., Experimental analysis of thermal runaway in 18650 cylindrical cells using an accelerating rate calorimeter, Batteries 3 (2017) 14, doi:10.3390/batteries3020014..
[3] A. Hofmann, N. Uhlmann, C. Ziebert, O. Wiegand, A. Schmidt, Th. Hanemann, Preventing Li-ion cell explosion during thermal runaway with reduced pressure, Appl. Thermal Eng. 124 (2017) 539-544.