The Effect of Entropy and Enthalpy Changes on the Thermal Behavior of Li-Mn-Rich Layered Composite Cathode Materials

The entropy changes (ΔS) and enthalpy changes (ΔH) of redox reactions occurring in the Li-rich, Mn-rich (LMR) layered composite cathode material Li1.2Ni0.15Co0.10Mn0.55O2 are systematically investigated using an electrochemical thermodynamic measurement system. The LMR cathode shows much higher ΔS than other conventional layered-structure cathode materials during the initial activation of the Li2MnO3 component associated with the concurrent extensive Li+ ion removal, oxygen evolution, and structural rearrangement. The evolution of entropy change during cycling correlates well with the transformation from layered to spinel-like phase. The reversible heat generation rate related to entropy changes dominates the thermal behavior of the LMR cathode at low rate conditions, especially during the initial charging process. The contribution of the reversible heat generation rate decreases in the subsequent cycles due to increased overpotential during cycling. These results provide valuable information on the fundamental mechanism of voltage fade in LMR cathodes and for thermal management of batteries using these materials.