Unveiling the aging memory effect in Lithium-ion batteries: A thermodynamic approach

We discovered that lithium-ion batteries (LIBs) retain a thermodynamic trace of their aging process, a phenomenon referred to here as the "aging memory effect." This memory effect can be revealed by measuring the entropy and enthalpy of aged cells at two well-defined open-circuit potentials (OCP): E10 = 3.87 V and E20 = 3.94 V. The study examined LIB cells consisting of graphite anode and lithium cobalt oxide (LCO) cathode. We observed that the variation in entropy and enthalpy at E10 and E20, strongly depends on the cells' aging history. E10 and E20 correspond to the potential onset of the phase transitions in the anode and cathode materials, respectively. These phase transitions serve as critical indicators that reflect the internal alterations and degradation mechanisms occurring within the battery over time. By meticulously monitoring the entropy and enthalpy changes at E10 and E20, we can retrace the battery's aging memory and identify the capacity-limiting electrode. Our findings indicate that these thermodynamic measurements can provide detailed insights into the electrodes' degradation pathways and phase transition behaviors. This knowledge is crucial for developing strategies to enhance the longevity and performance of LIBs.