For practical applications as the building envelope, the electrochromic device must have long-term durability. Figures and show the cycle test of the mid-IR emissivity tuning. The large emissivity contrast can be maintained for 1000 cycles and only degrade 21% after 1800 cycles, which exhibits a significant improvement from the previous reports using Ag-DMSO electrolyte (only up to 300~400 cycles). The emissivity spectra maintain their broadband feature after 2500 cycles (Figure ). It is noteworthy that the heating mode (low-e state) degrades faster than the cooling mode (high-e state), which could be attributed to the irrecoverable absorption of Cl -ions on the working electrode and the oxidation of the metal film. It should be mentioned that the deposition and stripping potentials are carefully selected to avoid hydrogen and oxygen evolution reactions (HER and OER). As shown in the cyclic voltammetry test (Figures and), there is no noticeable current increment related to HER or OER within the deposition and stripping potentials range for both 2-electrodes and 3-electrodes systems.