Abstract Electrolytically formed batteries (EFB) which start with a single composite between two current collectors, form positive and negative electrodes in situ theoretically allowing complex cell structures and low cost manufacturing. The fundamental challenge of charging shorts which heal upon removal of the current in electrolytically formed batteries is discussed in detail. In a demonstration EFB cell of LiI composite we show two unique routes towards solving this issue based on in situ formed solid electrolyte interfaces. The chemistry, physical and electrochemical characterization of such approaches are discussed. It is shown how these approaches have enabled the first demonstration of electrolytically formed solid state batteries and present a path to future improvement.