To achieve effective thermal management through the mid-IR modulation, an electrochromic device needs to perform the tunability in an extensive mid-IR range. Thanks to the high transmission of the graphene-based ultra-wideband transparent conductive electrode, the device can switch between the heating (low-e) and cooling mode (high-e) by depositing and dissolving the Cu film. Figure shows the Fourier-transform infrared spectroscopy (FTIR) of the device at two states. The building envelopes can switch between cooling mode (e 7.5-13μm ≈ 0.92) and heating mode (e 7.5-13μm ≈ 0.07). The thermal emissivity contrast of ∆e ≈ 0.85 is the highest among the reported non-mechanical mid-IR switching devices, including both thermochromic and electrochromic devices. (Figure ) The more detailed comparison is shown in Supplementary Information. (Table ) Non-volatile switching is another key criterion for smart building envelopes. Prior reports of Ag-DMSO electrolyte system require supplying a small bias to maintain the deposited (low-e) state, due to the excessive bromide and silver-bromide complex ions. This self-dissolution can lead to considerably low tuning efficiency at the low-e state because of the excessive electricity consumed to compensate for the loss of metal film. In contrast, the Cu-aqueous electrolyte can bypass this limitation by using the Cu 2+ /Cu (metal film) rather than the Br 3 -/Br -as the counter electrode redox couple. In Figure , 400 s negative bias of -0.7 V and -1.5 V were applied respectively on the electrochromic devices with Cuaqueous and Ag-DMSO electrolyte and subsequently left them at open-circuit. The as-deposited Ag film with the Ag-DMSO electrolyte quickly dissolved back into the electrolyte in only 100 s; in contrast, the as-deposited Cu film can stay for more than 5.5 hours in the Cu-aqueous electrolyte, confirmed by the stable low emissivity. This result allows us to safely assume that the electrical energy consumption to maintain the emissivity states is negligible and calculate the required annual electricity to switch the entire building envelope, as shown in Figure . The calculation method is described in Supplementary Note 1. The result shows that, even under the conservative assumption that the building envelope is switched three times a day with a large emissivity contrast of 0.80, the required annual electricity is negligible (only 0.13%) compared to the annual electricity usage of a baseline residential building. (59) , thermochromic hydrogel , electrochromic graphene devices #1(56) and #2 , electrochromic conductive polymer devices , and reversible electrodeposited Ag device . The comparison chart shows that our emissivity tunability range is the highest, with Δe = 0.85. (f) Non-volatility test of heating mode (metal-coated). Without the Br 3 -/Br -redox couple in the Ag-DMSO electrolyte, the electrochromic system can maintain its heating mode (low-e state) for 5.5 h without considerable decay. λ = 10 µm. (g) Annual electricity consumption for an aqueous device switching to different emissivity.