Retaining superior electrochromic performance by effective suppression of ion trapping upon cycling.

Smart windows based on electrochromic technology play a key role in decarbonization. However, cathodic electrochromic electrodes suffer from ion trapping induced performance degradation upon long-term cycling. Here, we present guidelines for designing electrolytes and preventing ion trapping to achieve optimal durability. Specifically, by controlling the solvation energy of the salts in the electrolyte, anions can be prevented from penetrating the cation-solvent sheath, thereby inhibiting their involvement in the ion trapping process. Therefore, cycling stability is significantly extended, i.e., no observed degradation after 1000 cycles. Following this concept, we further reveal that for the degraded electrodes which cannot be restored in an electrolyte with relatively weak cation-solvent interaction, they can be successfully recovered by switching to an electrolyte with strong cation-solvent interaction. Our work not only provides strategies to suppress the ion trapping and prolong the cycling stability of electrochromic electrodes, but also evokes the importance of electrode-electrolyte interaction to the electrochromic community.