Low　energy　density　hinders　the　development　of　supercapacitors　in　the　market　of　large　hybrid　power　equipment　and　electric　vehicles　that　demand　much　higher　energy　density.　Herein,　we　conduct　a　facile　and　environmentally　friendly　method　to　modify　the　electrodes　of　supercapacitors　through　coating　a　dielectric　thin　film　by　atomic　layer　deposition　(ALD)　technique,　which　profoundly　improves　the　electrochemical　performance　of　the　electrodes.　In　specific,　the　gravimetric　capacitance　of　the　ALD-Ti　modified　electrodes　is　characterized　by　35%　significant　promotion　comparing　to　the　commercialized　pristine　counterparts,　and　the　operational　voltage　window　of　the　ALD　treated　electrodes　can　expand　to　3.5　V　using　organic　electrolyte　with　remarkable　capacitance　retention　(over　83%)　even　after　20000　cycles.　Besides,　appropriate　models　are　established　to　discuss　the　detailed　charge　storage　mechanism　and　possible　reasons　for　good　stability　of　modified　electrodes　under　higher　operational　voltage.　Moreover,　the　excellent　rate　and　cycling　performance　of　ALD　modified　electrodes　in　flexible　electrochemical　double-layer　capacitor　(EDLCs)　at　the　bending　state　substantiates　the　application　superiority　of　ALD　modified　electrodes　in　flexible　devices.　The　unusual　combination　of　charge　storage　mechanisms　of　dielectric　capacitors　and　EDLCs　established　in　our　work　represents　specific　properties　in　great　need　for　energy　storage　applications.