Ionic　liquids　(ILs)　show　great　promise　to　endow　electric　double-layer　capacitors　(EDLCs)　with　high　energy　density;　however,　their　operation　in　practical　deep-cold　environments　has　been　severely　plagued　by　two　major　problems,　namely　(i)　poor　compatibility　between　the　electrode　material　and　the　ILs　and　(ii)　the　ease　of　freezing　of　ILs.　Here,　we　show　that　the　combination　of　a　nitrogen-doped　mesopore-dominated　hierarchical　carbon　(NMHC)　electrode　with　plentiful　ion-accessible　adsorption　sites　(specific　surface　area　and　pore　volume　of　2637.4　m(2)　g(-1)　and　1.679　cm(3)　g(-1))　and　anti-freezing　EMIBF4-GBL　electrolyte　with　high　ion-conductivity　(2.3　S　cm(-1)　at　-50　degrees　C)　can　address　this　issue.　Specifically,　＂H-bond　breakage＂　in　EMIBF4　ILs　was　proposed　for　the　first　time　to　understand　the　anti-freezing　mechanism,　as　evidenced　by　Raman　spectroscopy,　H-1　NMR　spectroscopy,　and　density　functional　theory　calculations.　As　a　result,　the　combination　of　NMHC　electrode　with　EMIBF4-GBL　electrolyte　enabled　an　impressive　specific　energy　of　61　W　h　kg(-1)　at　-50　degrees　C,　which　was　10.7　times　larger　than　that　of　commercial　YP50.　This　work　showed　excellent　electrode-electrolyte　synergy　and　provides　a　new　understanding　of　IL-based　electrolytes　for　low-temperature　energy　storage.