Coating layer design principles considering lithium chemical potential distribution within solid electrolytes of solid-state batteries

Introducing a coating layer at an active material /solid electrolyte interface is crucial for ensuring thermodynamic stability of the solid electrolyte at interfaces in solid-state batteries. To thermodynamically protect the solid electrolyte, coating layers must maintain lithium chemical potential (μLi) at coating layer/solid electrolyte interfaces within the electrochemical window of the solid electrolyte. However, a general coating layer design principle to achieve this remains unestablished. Here we theoretically elucidate the µLi distribution across the solid electrolyte and coating layer, examining requirements for thermodynamic protection. We show that the protective capability of coating layers is not solely determined by their intrinsic characteristics, but also by the µLi distribution within the solid electrolyte and coating layer. We propose a quantitative approach based on µLi distribution to determine the required characteristics and geometries of coating layers that ensure the thermodynamic stability of the solid electrolyte while minimizing ohmic resistance, providing insights for coating layer design. Coating layers are crucial for solid-state battery stability. Here, we investigated the lithium chemical potential distribution in the solid electrolyte and coating layer and propose a method to determine optimal coating layer properties, ensuring electrolyte stability while minimizing resistance.