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The electronic structures of bulk and (001) surfaces of λ-MnO2and LiMn2O4have been studied with density functional theory. In λ-MnO2, the Mn oxidation state is +4 both in the bulk and at the (001) surface. In LiMn2O4, however, Mn atoms exhibit mixed Mn3+/Mn4+oxidation states in the bulk, while only Mn3+at the (001) surface, due to lower coordination with O atoms. The technically undesired Mn3+ions form at LixMn2O4(001) even for very small Li concentrations. Upon covering the LiMn2O4(001) surface with Al2O3, the oxidation state of surface Mn atoms changes from +3 to +4, which explains the improved performance of coated LiMn2O4cathodes in Li-ion batteries.

Li2CO3, Li2O, and LiF are three important inorganic components that build up the “compact” layer of the solid electrolyte interphase which adhere tightly to the graphite anode of lithium ion batteries. The electrical conductivity and the lithium ion diffusivity within this layer are relevant to the rate performance of the graphite anode. Using density functional theory, the electronic structures of the three compounds are calculated and lithium migration dynamics are simulated using nudged elastic band method. Results show that all three components have insulating electronic structures, while lithium vacancies create some strongly localized holes that do not contribute much to the electronic conduction. Lithium diffusion in Li2CO3and Li2O can be very fast when lithium vacancies are available. The energy barriers of lithium migration in Li2CO3(ranges from 0.227 to 0.491 eV) and Li2O (0.152 eV) are comparable to that in graphite with the help of vacancies. However, lithium migration in LiF (energy barrier 0.729 eV) is much slower even when there are lithium vacancies in the lattice.