Electrochemical synthesis is a powerful tool for the preparation of conformal, thin solid electrolytes directly on the electrodes, particularly with complex shapes, such as nanostructured electrodes. Such separators should present the highest possible single ion conductivity, negligible electronic conductivity combined with high chemical and mechanical stability. These requirements drive our development work: we synthesize polymers with excellent mechanical properties, which are decisive for a high durability of the separators. The single-ion conductivity is assured by anchoring the counter-ions on the polymer backbone. The solid polymer electrolytes contain no flammable solvent guaranteeing high safety. For cation-conducting membranes, we synthesized polymers with sulfonate groups grafted on the macromolecular chain. These ionomers, including poly(styrene sulfonate) (PSS) can be used for proton exchange membrane fuel cells and Li batteries. Anion-conducting membranes contain quaternary ammonium as fixed cationic groups; they can be applied for example in hydroxide exchange membrane fuel cells. The paper presents the electrochemical synthesis procedures and the relevant structural, microstructural and electrical properties of cation- and anion-conducting polymers, including relevant data of applications, such as Li microbattery cycling.