Entropy Coefficient Evaluation of Lithium-ion Cells of Various Chemistry

Entropy coefficient, the key indicator of a lithiumion cell’s thermodynamic property. It represents reversible heat generation occurring during charge and discharge. Entropy profile of a lithium-ion cell is largely impacted by the anode/cathode chemistry as well as state of charge (SoC). Transitions of phase during lithium intercalation and deintercalation are accountable for the variation of the entropy coefficient. The entropy coefficient for lithium-ion cell is derived from potentiometric method. The experiments are carried out at full cell level for different chemistry such as NMC, LCO, NCA. Entropy coefficient is derived during discharge from 4.2 V to 3.0 V. Change in entropy coefficient at different temperatures is studied. Entropy coefficient of nickel-based cells turns positive to negative around $\mathbf{5 0 \% - 3 0 \%}$ SoC and consequently impacting the heat generation.