Interfaces in Solid Electrolyte Interphase: Implications for Lithium-Ion Batteries

The existence of passivating layers at the interfaces is a major factor enabling modern lithium-ion (Li-ion) batteries. The properties of the passivation layers determine the cycle life, performance, and safety of batteries. One critical passivation layer is the solid electrolyte interphase (SEI), a heterogeneous multicomponent film formed due to the decomposition of the electrolyte at the surface of the anode. The multicomponent nature is critical for its functioning as the interfaces between these components play a critical role in determining performance and safety. In this work, we use first-principles simulations to investigate the thermodynamic, kinetic, and electronic properties of the interface between lithium fluoride (LiF) and lithium carbonate (Li2CO3), two common SEI components present in Li-ion batteries with organic liquid electrolytes. We construct a coherent interface between these components that restricts the strain in each of them to below 3%. We find that the interfacial structure has a formation energy of the Frenkel defect higher than bulk calculations and similar to pristine Li2CO3, generating Li vacancies in LiF and Li interstitials in Li2CO3 responsible for transport. On the other hand, the Li interstitial hopping barrier is reduced from 0.3 eV in bulk Li2CO3 to 0.10 or 0.22 eV in the interfacial structure considered, demonstrating the favorable role of the interface. Controlling these two effects in a heterogeneous SEI is crucial for maintaining fast ion transport in the SEI. We further perform Car–Parrinello molecular dynamics simulations to explore Li-ion conduction in our interfacial structure, which reveal an enhanced Li-ion diffusion in the vicinity of the interface. Understanding the interfacial properties of the multiphase SEI represents an important frontier to enable next-generation batteries.