Space-Charge Effects at the Li₇La₃Zr₂O₁₂/Poly(ethylene oxide) Interface

Composites consisting of garnet-type Li₇La₃Zr₂O₁₂ (LLZO) ceramic particles dispersed in a solid polymer electrolyte based on poly(ethylene oxide) (PEO) have recently been investigated as a possible electrolyte material in all solid state Li ion batteries. The interface between the two materials, that is, LLZO/PEO, is of special interest for the transport of lithium ions in the composite. For obtaining the desired high ionic conductivity, Li⁺ ions have to pass easily across this interface. However, previous research found that the interface is highly resistive. Here, we further investigate the interface between Al-substituted LLZO and PEO-LiClO₄ electrolytes in the frame of a theoretical description, which is based on space-charge layers. By theoretical calculations supported by experiments, we find that the interface is highly resistive. From the results, we have deduced that the highest contribution to this resistance comes from a high activation energy and not from electrostatic repulsion of lithium.