Thermodynamic Analysis of LiNi<sub>0.6</sub>Mn<sub>0.2</sub>Co<sub>0.2</sub>O<sub>2</sub> (NMC622) Voltage Hysteresis Induced through High Voltage Charge
Wenzao Li, Lisa M. Housel, Garrett P. Wheeler, David C. Bock, Kenneth J. Takeuchi, Esther S. Takeuchi, Amy C. Marschilok
Abstract
High voltage charge of NMC materials can extend the initial capacity but also impair the long-term cyclability. This investigation probes NMC622 with charge limits of 4.3 and 4.7 V using operando isothermal microcalorimetry. A higher voltage charge to 4.7 V brings ∼17% increase in capacity yet a doubling of the heat dissipated compared to 4.3 V. Additionally, the thermodynamic paths of (dis)charge visualized by enthalpy potential show path-dependent (de)lithiation in the 3.0–4.7 V window. More evidence is provided explaining the long-term energy fading of NMC622 induced by high voltage, including increased thermal energy waste and asymmetric (de)lithiation thermodynamics.