Abstract: A composite solid electrolyte for a solid-state electrochemical cell is provided. The electrolyte may include a plurality of aramid nanofibers, such as a branched aramid nanofiber network, an ionically conductive polymer, such as poly(ethylene oxide) or quaternary ammonia functionalized polyvinyl alcohol (QAFPVA), and an optional divalent ion salt. The electrolyte is particularly suitable for use with zinc ions, where the divalent ion salt may comprise zinc trifluoromethanesulfonate Zn(CF3SO3)2 An electrochemical cell or battery is provided incorporating such a composite solid electrolyte that cycles ions, such as zinc ions or hydroxide ions, suppresses or minimizes dendrite formation, while having good ionic conductivity and being flexible. This flexibility provides the ability to create deformations in the electrochemical cell, such as protrusions and recesses that may define a corrugated pattern.