Abstract: Amphiphilic complexing agents for use in electrolyte solutions are provided. The complexing agents include at least one soft ionic group covalently bonded to at least one hard ionic group or polyether chain. The soft ionic group couples with soft, oppositely charged ionic redox species in an electrolyte solution, and the hard ionic groups or polyethylene chains render the complexes formed by the complexing agents and ionic redox species soluble in the electrolyte solution. The size of the complex formed by the coupling of the amphiphilic complexing agent to the soft ionic redox species is substantially larger than the size of the soft ionic redox species alone and, as a result, electrochemical cells that include the amphiphilic complexing agents in an electrolyte solution have less membrane crossover than analogous electrochemical cells that do not include the amphiphilic complexing agents.