The temperature of a lithium-ion battery is a crucial parameter for understanding the internal processes during various operating and failure scenarios, including thermal runaway. However, the internal temperature is comparatively higher than the surface temperature. This particularly affects cells with a large cross-section, which is due to heat development within the cell and lower heat dissipation due to a poorer ratio of volume to surface area. This paper presents an approach that enables real-time monitoring of the behavior of a commercial prismatic high-energy battery cell (NMC811/C, 95 Ah, Contemporary Amperex Technology Co., Limited (Ningde, China)) in the event of thermal runaway induced by overcharging. The internal cell temperature is investigated by the subsequent integration of two hard sensors between the two jelly rolls and additional sensors on the surface of the aluminum housing of the battery cell. The sensor’s signals show a significant increase in the temperature gradient between the temperature in the core of the cell and the cell casing surface until the onset of venting and thermal runaway of the battery. The data enable a detailed investigation of the behavior of the battery cell and the comparatively earlier detection of the point of no return in the event of thermal runaway.

Die Zustandsbewertung von Batterien vom Gesamtsystem bis hin zur Zellebene stellt vor allem außerhalb des Laborumfelds weiterhin eine Herausforderung dar. Die in der Zelle ablaufenden Alterungsmechanismen überlagern sich auf komplexe Weise, was eine eindeutige Ursachenanalyse erschwert. Neben den elektrischen Charakterisierungsmethoden bieten die mechanischen Ansätze vielversprechende Möglichkeiten, bislang ungenutztes Potenzial zur Verbesserung der Datenverfügbarkeit und Transparenz zu erschließen.

Lithium-ion batteries (LIBs) are considered a pivotal enabling technology for the advancement of transportation electrification, the development of stationary energy storage systems, and the integration of renewable energy sources. Despite continuous advances in energy density and cell design, the fast-charging capability of LIBs is still significantly constrained by temperature-dependent electrochemical and thermal processes, which are crucial to the overall performance of the battery. The objective is to quantify the temperature-dependent fast-charging potential and charging power capability. This is achieved by experimentally analyzing the internal resistance (IR) during the charging of three large-format prismatic state-of-the-art cells, in addition to extrapolating their charging power capability and constant-current constant-voltage charging behavior under varying thermal boundary conditions. Utilizing the IRs ascertained during the charging process, the fast-charging potential (FCP) is introduced as a dimensionless metric that expresses the temperature-induced increase in the maximum theoretically achievable charging current at a given SoC, relative to 25 °C. Elevated cell temperatures are found to reduce IR and thus increase the theoretically achievable charging power, with the FCP nearly independent of SoC but cell-specific, ranging from about 18% (CATL) to 40% (SVolt) for a temperature increase from 25 °C to 45 °C. This potential can be exploited in two ways: firstly, by increasing the C-rate while maintaining the same constant-current duration; and secondly, by extending the constant-current phase at a constant initial C-rate. The proposed methodology facilitates a systematic and comparative evaluation of the maximum theoretically attainable temperature-dependent fast-charging potential of LIBs. It provides a foundation for the development of thermally optimized fast-charging strategies.