Heat dissipation in a lithium ion cell

A comparative study of the heat dissipated by a 3.3 A h LixC/LiNiO2 cell and a 1.25 A h LixC/75% LiCoO2, 25% LiNiO2 cell was conducted through experimental heat rate measurements using a radiative calorimeter. The specific heat of the cell was determined experimentally to be 0.969 J/°C g for the LiNiO2 cell and 0.946 J/°C g for the LixC/75% LiCoO2, 25% LiNiO2 cell. The LixC/LiNiO2 cell had a higher self-discharge rate than the LixC/75% LiCoO2, 25% LiNiO2 cell. The heat dissipated during discharge increased with the rate of discharge. During charge, initial endothermic cooling and subsequent exothermic heating beyond 55% state-of-charge were observed. At the C/2 rate of discharge (medium rate), the heat dissipated was 17 mW/cm3 for the LixC/LiNiO2 cell and 11.2 mW/cm3 for the LixC/75% LiCoO2, 25% LiNiO2 cell. The experimental values obtained for the heat dissipation at various charge and discharge rates were used to calculate thermoneutral potentials of 3.698 and 3.836 V for the LixC/LiNiO2 and LixC/75% LiCoO2, 25% LiNiO2 cells, respectively. The proposed values for thermoneutral potential may explain the endothermic cooling during charge and the negative temperature coefficient for cell voltage.