**In-Operando Impedance Spectroscopy and Ultrasonic Measurements during High-Temperature Abuse Experiments on Lithium-Ion Batteries**

#### **Hendrik Zappen 1,2,3,\*, Georg Fuchs 1,2,3 and Alexander Gitis 1,2,3 and Dirk Uwe Sauer 1,2,4,5**


Received: 9 March 2020; Accepted: 18 April 2020; Published: 22 April 2020

**Abstract:** Lithium-Ion batteries are used in ever more demanding applications regarding operating range and safety requirements. This work presents a series of high-temperature abuse experiments on a nickel-manganese-cobalt oxide (NMC)/graphite lithium-ion battery cell, using advanced in-operando measurement techniques like fast impedance spectroscopy and ultrasonic waves, as well as strain-gauges. the presented results show, that by using these methods degradation effects at elevated temperature can be observed in real-time. These methods have the potential to be integrated into a battery managemen<sup>t</sup> system in the future. Therefore they make it possible to achieve higher battery safety even under the most demanding operating conditions.

**Keywords:** EIS; electrochemical impedance spectroscopy; lithium-ion batteries; characterization; diagnostics; abuse test; high temperature; degradation; safety; ultrasonics; ultrasound; strain; gassing; gas evolution
