One subject of the invention is an isolating device (10) for electrically isolating a plurality of power-storage assemblies (102) placed side-by-side in a power-storage module (100) from one another, the device comprising a sheet (11) made of an electrically insulating material lying in a main plane (P), the device also comprising at least one tongue (12A-12E; 14A-14E, 16A-16E, 18A-18D, 20A, 20D, 22A-22D) integral with the sheet (11) and capable of protruding from the main plane (P) of the sheet by extending essentially perpendicularly to said main plane of the sheet. Another subject of the invention is a module comprising at least one of these devices.