Thermal behavior of aged lithium-ion batteries: calorimetric observations

Aging-induced changes of thermal behavior in highpower cylindrical lithium-ion battery cells are quantified by adiabatic calorimetry. Cells were aged by cycling with different charge currents. Changes in impedance and entropy profile are observed as consequence of prolonged cycling. Accelerating Rate Calorimeter (ARC) is used to determine heat capacity of the cells and to measure their temperature during discharge in adiabatic mode. This facilitates accurate calculation of heat generation during discharge. Using entropy and impedance data, shares of reversible and irreversible contributions to heat generation are estimated. Results elucidate the complex relationship between cell aging conditions and resulting thermal behavior and energy efficiency. Cells at similar state of health (usually understood as remaining capacity) exhibit notably different energy efficiencies and thermal behavior during discharge. The total number of charge-discharge cycles is shown to be crucial aging parameter contributing to increased heat generation during discharge and thus reducing the energy efficiency of the cells.