Free Energy for Protonation Reaction in Lithium-Ion Battery Cathode Materials

Calculations are performed of free energies for proton-for-lithium-ion exchange reactions in lithium-ion battery cathode materials. First-principles calculations are employed for the solid phases and tabulated ionization potential and hydration energy data for aqueous ions. Layered structures, spinel LiMn2 O4, and olivine LiFePO4 are considered. Protonation is most favorable energetically in layered systems, such as Li2 MnO3 and LiCoO2. Less favorable are ion-exchange in spinel LiMn2 O4 and LiV3 O8. Unfavorable is the substitution of protons for Li in olivine LiFePO4, because of the large distortion of the Fe and P coordination polyhedra. The reaction free energy scales roughly linearly with the volume change in the reaction.