Polyanionic electrolytes with high alkali ion conductivity

Abstract

We describe the synthesis of chain polymers that contain Lewis base or Lewisacid groups in the backbone that can then be reacted with acidic or basicgroups to form polyanions with weak binding sites for alkali cations. Wereview both `base-in-chain' and `acid-in-chain' approaches to this type ofpolyanion. When the anionic groups are optimally separated, the conductivitiesof the polymers are found to be high relative to those of most single ionicconducting polymers and even most non-imide salt-in-polymer electrolytes. Theconcentration of ionic groups, can be varied using polyethylene glycol links(spacers) of variable length. The conductivity is found to maximize near thevalue which maximizes the conductivity in simple salt-in-fully amorphouspolyether polymers (the number of the ethyleneoxy repeating unit n = 12).Finally a novel process, which achieves the same objective by a differentroute, will be described. This class of weakly coordinating polyanionicelectrolyte, in which the coulomb traps for Li+ are little if at allstronger than the polyether chelation traps, is seen as a promisingdevelopment in the solid polymer electrolyte field. Except for the case of`weak trap' acid-in-chain polymers, all these electrolytes are unicationic intheir conduction.