Operando X-ray Diffraction during Battery Cycling at Low Temperatures

Kurzfassung

Lithium-ion batteries are nowadays widely used in consumer electronics and electric vehicles. However, the application in electric vehicles poses new challenges to this battery technology. High energy and power densities, a high degree of safety and a long lifetime are important to meet the requirements of the customers. To improve lithium-ion batteries, it is necessary to gain a deeper understanding of electrochemical processes occurring during battery cycling. Operando characterization techniques are used to shed light on these processes. In particular, operando X-ray diffraction (XRD) and neutron diffraction are applied for the observation of phase changes of battery materials during cycling. Thereby, the lithiation and delithiation mechanism can be investigated depending on different factors like C-rate or temperature. The gained deeper understanding of the structural behavior of battery materials under various operating conditions leads to the improvement of battery management systems by increasing the performance and reducing degradation processes of batteries. The phase changes of state-of-the-art battery materials at room temperature are well understood but the influence of temperature on the phase evolution is barely investigated. Recent studies show that the classical staging mechanism of graphite [1, 2] does not occur at higher C-rates [3, 4] and elevated or low temperatures [5, 6] and instead, several stages coexist. During a rest period after charge or discharge, these phases can equilibrate [6]. The lithiation and delithiation mechanism does not only influence the charge and discharge behavior, but also the dimensional changes concurrently with the degradation of the electrodes [5]. Therefore, a deeper understanding of the structural behavior of battery materials under various operating conditions is needed to improve the material properties and adapt battery management systems to increase the performance of the battery and reduce degradation. At DLR, a new set-up was developed to investigate with operando XRD the phase evolution of battery materials during cycling at temperatures below room temperature. This method allows a readily characterization of battery materials at various temperatures and the identification of the temperature dependent intercalation mechanisms.