Mechanism of Li+ charge transfer at Li/Li7La3Zr2O12 interfaces: A density functional theory study

Interfacial charge transfer kinetics between solid electrolyte (SE) and Li metal in all-solid-state Li-ion batteries is one of the limiting factors for their practical use. The mechanism of interfacial charge transfer is still poorly understood. In this work, we study the Li-ion charge transfer at interfaces between perspective SE of garnet-type ${\mathrm{Li}}_{7}{\mathrm{La}}_{3}{\mathrm{Zr}}_{2}{\mathrm{O}}_{12}$ (LLZO) and Li metal, utilizing the density functional theory and nudged elastic band method (DFT-NEB). We demonstrate that it is crucial to consider the relatively long percolating conduction pathway through the interface. Due to the formation of energy minima for Li vacancies, the activation energies for ${\mathrm{Li}}^{+}$ charge transfer additionally increase by 0.1--0.3 eV compared with ${\mathrm{Li}}^{+}$ migration barriers in bulk LLZO. We show that the formation of interfacial energy minima is because of the electronic density redistribution from the metallic Li to the LLZO region. These results improve our understanding of interfacial charge transfer in solid-state batteries with metallic lithium.