Lithium deposit morphology has been observed for polymer electrolytes employing ethylene oxide (EO)-propylene oxide (PO) copolymers as host polymers. The effects of polymer compositions such as the host polymer skeleton, the weight ratio of host polymer to liquid electrolyte, etc. were studied on suppressing dendritic morphology of lithium deposition. To suppress dendrites, stiff and elastic polymer electrolytes were suitable, which employed host polymers with ($) over bar Mw > 16000 before cross-linking and EO/PO < 5 and contained liquid electrolyte of less than 70 wt%.