Correlation between electric and mechanical/thermal parameters in a graphite - LiFePO4 Li-ion pouch cel

The operation of a lithium-ion battery (LIB) cell is governed by the much desirable periodicity and reversibility of lithium ions extraction and insertion mechanisms, as they are transported between the electrodes, keeping the capacity retention high. Unavoidably, there is an irreversible part manifested as capacity loss due to solid electrolyte interphase (SEI) growth, contact loss, active material deterioration, and lithium inventory loss, factors that are extensively documented and studied, mainly through the electric parameters of current, voltage, and charge from cell level to commercial operating battery packs [1]. The significance of monitoring volume changes in LIB stacks, accompanied by a corresponding stress development, is primordial in order to understand the phenomena that lead to degradation and performance decline.
Towards this direction, the correlation of thermodynamic parameters with the commonly studied electric parameters in grahite/LFP lithium-ion battery cells provides important information. From the comparison of stored charge, incremental capacity peak intensity and position and state of health against pressure it can be revealed that there is a strong connection between pressure and peak intensity. The evolution of cell pressure with cycles justifies this relation, however, the cell temperature obeys the joule effect following the current variations. It was found that the normalized pressure varies almost linearly with the State of Charge (SoC) in different parts of the charging curve. This cycle-to-cycle normalized pressure data analysis could potentially be incorporated in a battery management system to provide accurate SoC indications.