At present, the only commercial lithium-metal battery (LMB) technology is based on polyethylene oxide (PEO) based electrolytes. However, its limited ionic conductivity at ambient temperatures requires the operation (discharge and charge) at elevated temperatures of around 60 ◦C–80 ◦C, i.e., close to and above the melting point of PEO. Herein, we investigate the impact of incorporating varying amounts of tetraethylene glycol dimethyl ether serving as chemically identical plasticizer to enhance the ionic conductivity also at lower temperatures. A comprehensive comparison of the physicochemical, electrochemical, and mechanical properties is conducted via complementary experimental and theoretical studies, with a particular focus on the impact on the morphology of the deposited lithium using ex situ X-ray tomography. The results reveal that the mechanical properties play a key role for achieving
a homogeneous and smooth lithium deposition. These insights are anticipated to contribute to further optimized polymer-based electrolytes for next-generation LMBs