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

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 Delta G(process) as a function of SoC(c) at two different porosities of 0.25 and 0.4 was also attempted via thermodynamic analysis.