Thermodynamic insights into the free energy of the processes in lithium iron phosphate batteries

Abstract

The evaluation of energetics involved in the discharge of LiFePO₄-based lithium-ion batteries (LiBs) was written in terms of solvation, diffusion, phase transition and porosity parameters. LiFePO₄ undergoes single phase transition from FePO₄ to LiFePO₄ without involving any major structural change. The phase transition energetics of FePO₄ to LiFePO₄ was evaluated to be −3.84 eV by the current methodology. The results were consistent with those of the core–shell energetics reported in the literature. The free energy required for the discharge of LiBs converged at around −1.77 eV at SoC_c = 0.3 irrespective of the variation in porosity. This convergence was attributed to the solid electrolyte interface (SEI) formation energetics at the anode/electrolyte interface via the thermodynamic approach. The physical significance of ΔG_process as a function of SoC_c at two different porosities of 0.25 and 0.4 was also attempted via thermodynamic analysis.