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 O-4, and olivine LiFePO4 are considered. Protonation is most favorable energetically in layered systems, such as Li-2 MnO3 and LiCoO2. Less favorable are ion-exchange in spinel LiMn2 O-4 and LiV3 O-8. 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.