Heat Generation in NMC622 Coin Cells during Electrochemical Cycling: Separation of Reversible and Irreversible Heat Effects
Wenjiao Zhao, Magnus Rohde, Ijaz Ul Mohsin, Carlos Ziebert, Hans Seifert
Abstract
The thermal behavior of a commercial lithium-ion cell with the cathode material LiNi0.6Mn0.2Co0.2O2 (NMC622) was investigated during the cycling process using a Tian-Calvet calorimeter (C80, SETARAM Instrumentation, France). Various current flows of 42.5, 85, and 170 mA corresponding to charging rates of 0.5, 1, and 2 C, respectively, were applied in the measurements. The corresponding heat flow rates were measured by the C80 calorimeter at 30 °C. The reversible heat effect due to the reversible electrochemical reaction was quantified by the entropy change measurement. The irreversible heat effect due to internal resistances was determined by the electrochemical impedance spectroscopy (EIS) and the galvanostatic intermittent titration technique (GITT). The results were compared with the direct measurement of the heat effect by calorimetry during electrochemical cycling.