Thermodynamic Analysis of LiNi_0.6Mn_0.2Co_0.2O₂(NMC622) Voltage Hysteresis Induced through High Voltage Charge

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.