Abstract: A solid electrolyte including zwitterionic compounds comprising zwitterionic molecules and/or charge neutral polymers with zwitterion pendants. A salt is distributed through the solid such that the solid conducts alkali metal ions obtained from the salt and the zwitterionic compounds each include zero or more amorphous regions and one or more crystalline regions characterized by (1) a presence of Bragg diffraction peaks in an X-ray diffraction measurement of the solid; and (2) the solid having an ion conductivity of at least 10?4 S/cm at a temperature of 50 degrees Celsius when a transport number for the alkali metal ions is at least 0.5 and a molar ratio of the salt to the zwitterionic units is 0.9. The electrolyte exhibits surprisingly high alkali metal ion conductivity and linear elastic modulus over a wide range of practically useful temperatures.