Hans J. Seifert, Ph.D., Professor & Head, Institute for Applied Materials (IAM-AWP), Karlsruhe Institute of Technology (KIT) was interviewed recently by CET.

His KIT colleague Carlos Ziebert, Ph.D., Senior Scientist, Head of the KIT Battery Calorimeter Center, is a presenter at both the 13th Annual Lithium Battery Materials & Chemistries and 8th Annual Battery Safety conferences in Arlington, Virginia this October 31–November 3.

Lithium-Ion Battery Safety Measurements: Using Battery Calorimetry, Improving Thermal Stability, and Providing Quantitative System-Relevant Data

1) What led you to your current Li-ion battery safety and thermochemical research, and what resources at KIT’s Institute for Applied Materials enable it?

An important focus of our work is on thermochemical and safety studies of electrochemical cells/batteries and their active materials by experiments and modeling. The institute now operates one of the world's largest battery calorimeter laboratories. In operation are five Accelerating Rate Calorimeters (ARC) of different sizes, an isothermal battery calorimeter, several temperature chambers, a thermal camera and cell testers including electrochemical impedance spectroscopy (EIS). Additionally, four Differential Scanning Calorimeters (DSC), several Tian-Calvet Calorimeters as well as Laser flash facilities are available. In the ARC, safety tests for simulated cases of non-regular battery use and accidents (thermal runaway, overcharging, internal/external short circuit, mechanical impact) are performed. Furthermore, cells of varying aging states can be opened for post-mortem analyses in glove boxes and characterized by means of numerous materials science analysis tools.

As one result of the investigations, quantitative system-relevant data for temperature, heat and pressure development of batteries are provided. These data are used by both our research and industrial partners for the design of thermal management and safety systems. For modeling and of thermal transport and thermodynamic properties (Computational Thermodynamics, CALPHAD), specific heats (heat capacity), thermal conductivities, enthalpies and correlated electrochemical data are measured. The results serve as input data for simulations on materials and cell level, respectively. The simulation of cell behavior is done with finite element modeling (FEM, Software: Comsol Multiphysics) or equivalent circuit models (ECM, Software: Matlab Simulink, MapleSim). With these facilities, and the established technical and methodological expertise, the IAM-AWP is one of the few worldwide institutions that investigate simultaneously thermodynamics and related thermal and safety properties of batteries and their materials.

2) What do you consider the most useful measures of battery safety?

To avoid thermally induced reactions, the battery systems have to be designed for optimized safety on the material, cell and pack level, respectively. Therefore, the (thermal) battery management and cooling systems must be perfectly tailored to technical and commercial requirements. Thus the complete fundamental scientific and technical understanding of these effects is of upmost importance. Safety is an important selection criterion for the cell chemistry, specific cell design and battery packs.

At the IAM-AWP, research projects are conducted with a twofold focus: on the materials development for all solid-state cells and on the analysis and characterization of thermal effects and safety in Li-ion cells. The common objective of these studies is the improvement of thermal stability towards an inherently safe cell and battery pack.

3) What areas have shown the most promising progress in Li-ion safety measurements, prediction and prevention?

For an optimized design with regard to safety cells, pack and batteries have to be quantitatively characterized not only for their temperature behavior but also for both their heat generation and dissipation. Therefore, the battery calorimetry has shown the most promising progress in safety measurements, because it allows collecting quantitative data on temperature (rates), heat (rates) and on the internal pressure development while operating the cell under conditions of normal use, abuse or accidents. These data are essential input for the knowledge-based design of battery management systems, thermal management and safety systems.

4) Why have you chosen to speak at both conferences on Lithium Battery Materials & Chemistries and Battery Safety, and what do you intend to convey to the audience through your presentations?

It is clear that the development of a safer and more powerful battery has to start with a reasonable materials choice, therefore the topics of both conferences are related to each other and represent perfectly the research directions of our institute in the field of lithium batteries. We are especially interested in all thermodynamic/thermophysical properties of active materials as the underlying data to quantitatively evaluate full cell and battery safety performances. Therefore, I have chosen to speak at both conferences in order to show our results in both areas – individual materials properties and their behavior in the operating systems. From the presentation at the Lithium Battery Materials & Chemistries conference, the audience will have insights into the use of calorimetry to receive data for the heat capacities and enthalpies of formation for phases within the solid solution series of, e.g., NMC cathode materials. It will be shown how these data correlate to the materials electrochemical behavior and stability as well as the specific crystal chemistry. From the presentation at the Battery Safety conference, the audience will get insights into the use of battery calorimetry to record thermal and safety data. It will be made clear how these data help to understand the exothermic reactions triggering thermal runaway and how this helps to develop safer cells and batteries.

Interviewee Information:

Hans Seifert is head of the Institute for Applied Materials (IAM-AWP) at the Karlsruhe Institute of Technology (KIT) and Professor in Materials Science and Engineering. He received his Ph.D. from University of Stuttgart, Germany, in 1993. He then served as a research group leader for Materials Thermodynamics at the Max Planck Institute for Metals Research, Stuttgart. From 2001 to 2003 he worked as a Senior Coating Expert for Alstom (Switzerland) and from 2003 to 2006 as an Associate Professor at the Department of Materials Science and Engineering, University of Florida, USA. In July 2006 he was appointed Professor by the Technical University of Freiberg, Germany. Since January 2011 he has been working for Karlsruhe Institute of Technology. He is speaker of a Priority Programme of the German Research Foundation: "Materials with New Design for Improved Lithium Ion Batteries" and served as coordinator of the EERA Joint Programme "Energy Storage".

Presentations by KIT colleague Dr. Carlos Ziebert:

“Thermochemical Investigations of LiNixMnxCo1-2xO2 (0≤x≤0.5) Phases (NMC)”

Tuesday, October 31 during the Lithium Battery Materials & Chemistries conference.

“Thermal Runaway of Lithium Batteries Analyzed by Accelerating Rate Calorimetry and Thermography”

Friday, November 3 during the Battery Safety conference.