Aqueous electrochromic battery (ECB) is a multifunctional technology that shows great potential in various applications including energy-saving buildings and wearable batteries with visible energy levels. However, owing to the mismatch between traditional electrochromic materials and the electrolyte, aqueous ECBs generally exhibit poor cycling stability which bottlenecks their practical commercialization. Herein, we present an ultrastable electrochromic system composed of lithium titanate (Li4Ti5O12, LTO) electrode and Al3+/Zn2+ hybrid electrolyte. The fully compatible system exhibits excellent redox reaction reversibility, thus leading to extremely high cycling stabilities in optical contrast (12 500 cycles with unnoticeable degradation) and energy storage (4000 cycles with 82.6% retention of capacity), superior electrochromic performances including high optical contrast (∼74.73%) and fast responses (4.35 s/7.65 s for bleaching/coloring), as well as excellent discharge areal capacity of 151.94 mAh m–2. The extraordinary cycling stability can be attributed to the robust [TiO6] octahedral frameworks which remain chemically active even upon the gradual substitution of Li+ with Al3+ in LTO over multiple operation cycles. The high-performance electrochromic system demonstrated here not only makes the commercialization of low-cost, high-safety aqueous-based electrochromic devices possible but also provides potential design guidance for LTO-related materials used in aqueous-based energy storage devices.
CsPbX3 (X = Cl, Br, I) perovskite nanocrystals (NCs) have shown great potential in numerous applications including wide color gamut display and lighting. Despite the wonderful luminescence properties, the inherent instability of these NCs hinders their use in practical situations. Herein, we report a facile aqueous-based, ligand-free method to synthesize highly stable CsPbX3 NCs using ZIF-62, a metal–organic framework, as an encapsulation matrix which effectively isolates CsPbX3 from the surrounding. We discovered that the slightly alkaline nature of ZIF-62 facilitates the reaction between water and PbBr2 to form PbBr(OH), which not only passivates the surface defects of the CsPbBr3 NCs but also prevents the perovskite from decomposing or oxidizing at high temperature. Sintering of ZIF-62 can therefore be performed in air at ∼300 °C to completely seal the perovskite within the insulating matrix, resulting in CsPbBr3/ZIF-62 composites exhibiting high stability against polar solvents, heat, light, and ambient humidity. Notably, the composite can maintain its bright luminescence without noticeable degradation in water for more than 2 months. The narrow-band emission and stability of these composites led to the demonstration of white light-emitting diodes with excellent color stability. Without the need for organic solvents during NC synthesis and noble gas ambient during sintering, the strategy proposed here can potentially facilitate the cost-effective, large-scale synthesis of highly stable perovskites which show great promise in commercial applications.
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