Poly(ethylene oxide) (PEO)-based Zn(II) halide electrolytes with optimized compositions exhibit rather high conductivities compared to other PEO solutions of divalent cation salts. Chemical diffusion studies have clearly demonstrated that both Zn(II) and Br(-I) are mobile. It appears that Zn(II) cations occur in two forms, one associated with the ether oxygens and another associated with the anions. It is reasonable that the former should be less mobile than the latter. Regrettably, quantitative measurement of the transference number and diffusion coefficients of the charge carriers using electrochemical techniques proved difficult. Other measurements found that the value of Tg for the completely amorphous forms of the electrolytes increases linearly with the mole ratio of Zn/O, indicating that Zn(II) cations interact with ether oxygens in the PEO chains to form inter- and/or intrachain crosslinks. © 1991, The Electrochemical Society, Inc. All rights reserved.