Work Package 4: Safer Batteries

(Updated: March 2020)

OBJECTIVES

Improving the safety of Li-ion batteries in electric vehicles.

PARTNERS

PARTNERS: CEA (Lead), TUM, TUV SUD, Algolion, RWTH

APPROACH

• Improve the in-depth understanding of internal short circuits and thermal runaway mechanisms and their consequences in a battery module. This will be done using post-mortem analysis of battery cells and experimental validation of electrical & thermal modelling and diagnostics at cell & module scales. Based on this deeper understanding, algorithms can be optimized to define safer operating ranges (I,V,T).
• Detect precursors to thermal runaway using novel proactive methods to enable implementation of measures starting days in advance that can prevent thermal runaway, halt its propagation or mitigate its effect thanks to the development of multi-sensing strategies and algorithms.

RESULTS SO FAR

ALGOLiON:

1. Development of method to create lithium plating and to validate that it occurred via use of the early warning diagnostic algorithm. This validation was supported by conventional electrochemical methods (e.g., observing a high voltage stripping plateau on discharge subsequent to the charge cycle that produced the plating, and chemical analysis.
2. Development of a method to reproducibly drive cells into thermal runaway using an external point  contact heating technique. The point contact simulates heat generation caused by lithium dendrites that short the cell by electrically bridging between the anode and the cathode.

CEA:

1. The proposed multi-sensing capability for monitoring of Li-ion cells has been validated for three basic battery abuse cases (Thermal abuse ; Short-circuit abuse ; Overcharge abuse). The measurements of the cell casing deformation (strain gages sensor) associated to electrical and thermal sensors and an associated signal processing appears to be very a promising, rapid and generate early indicator of risk of thermal runaway (almost 30 minutes in advance for some cases).
2. Two multi-physic models of thermal runaway propagation have been developed at cell and module scale. Those models give the opportunity to get a better understanding of the chronology of physical events and to quantify the impact of design change on the risk of thermal runaway propagation.
3. In situ XRD measurements on overcharged cells have been performed and the results are consistent with ex-situ studies.

TÜV SÜD:

1. In order to perform the required cell abuse tests to provide data to the relevant EVERLASTING partners, TÜV SÜD successfully implemented an abuse method to create a soft internal short circuit within a tested cell using a crush-device and a control loop closely monitoring the cell voltage.