A separator for a flowing electrolyte battery, and a method of forming such a separator, enable improved efficiency in a flowing electrolyte battery. The separator includes a sheet having a first surface and a second surface opposing the first surface. A first spacer element is disposed on the first surface, and a second spacer element is disposed on the second surface. The first spacer element is wider than the second spacer element in a direction that is both parallel to the first and second surfaces and perpendicular to longitudinal axes of the first and second spacer elements.