Impact of Amorphous LiF Coating Layers on Cathode-Electrolyte Interfaces in Solid-State Batteries

High interfacial resistance between electrodes and solid-state electrolyte is the major cause for the failure of all-solid-state Li-ion batteries. Spontaneous (electro)chemical reactions and poor Li-ion diffusion at the interfaces are closely related to this increased impedance. Although introducing a coating layer can mitigate interfacial reactions and structural reconstruction, it may also lead to poor Li-ion diffusion. Balancing this trade-off therefore is crucial for the design of coating layer materials. In this study, the impact of the amorphous LiF (a-LiF) coating layer on interfacial structural reconstruction and Li-ion diffusion at the LiCoO2/Li6PS5Cl solid-state interface is explicitly elucidated via machine-learning-assisted molecular dynamics (MD) simulations. It is found that the a-LiF can effectively protect the P-S tetrahedron local structures in Li6PS5Cl but cannot suppress the formation of side product S2 dimers. It is further discovered that once the a-LiF coating exceeds a certain critical thickness, emergence of ordered local structures will inhibit Li-ion diffusion. The simulations propose that the optimal thickness of the coating layer is around 1 nm. Overall, the work provides a microscopic understanding for effects of the a-LiF coating layer on the structural and kinetic properties of cathode-solid electrolyte interfaces and can guide the design of interfacial coating materials for solid-state batteries. This research elucidates the impact of the amorphous LiF coating layer on interfacial structural reconstructions and Li-ion diffusion in the LiCoO2/Li6PS5Cl solid-state interface via large-scale machine-learning-assisted molecular dynamics simulations, which can guide the design of interfacial coating materials for solid-state batteries. image