A Low Driving-Voltage Hybrid-Electrolyte Electrochromic Window with Only Ferreous Redox Couples.

Even after decades of development, the widespread application of electrochromic windows (ECW) is still seriously restricted by their high price and inadequate performance associated with structural/fabrication complexity and electrochemical instability. Herein, a simple hybrid electrochromic system based on PFSA (perfluorosulfonic acid)-coated Prussian blue (PB, Fe4III [FeII(CN)6]3) film and Ferricyanide-Ferrocyanide ([Fe(CN)6]4-/[Fe(CN)6]3-)-containing hybrid electrolyte is reported. The PB film and the [Fe(CN)6]4-/[Fe(CN)6]3- couple show near redox potentials well inside the electrochemical window of water, resulting in a low driven voltage (0.4 V for coloring and -0.6 V for bleaching) and a relatively long lifespan (300 cycles with 76.9% transmittance contrast retained). The PFSA layer, as a cation-exchange structure, significantly improves the transmittance modulation amplitude (ΔT: 23.3% vs. 71.9% at a wavelength of 633 nm) and optical memory abilities (ΔT retention: 10.1% vs. 67.0% after 300 s open-circuit rest increases) of the device, by means of preventing the direct contact and charge transfer between the PB film and the [Fe(CN)6]4-/[Fe(CN)6]3- couple. This "hybrid electrolyte + electron barrier layer" design provides an effective way for the construction of simple structured electrochromic devices.

Boosting Zn||I2 Battery's Performance by Coating a Zeolite-Based Cation-Exchange Protecting Layer.

HIGHLIGHTS: High-performance Zn||I2 batteries were established by coating zeolite protecting layers. The Zn2+-conductive layer suppresses I3- shuttling, Zn corrosion/dendrite growth. The Zeolite-Zn||I2 batteries achieve long lifespan (91.92% capacity retention after 5600 cycles), high coulombic efficiencies (99.76% in average) and large capacity (203-196 mAh g-1 at 0.2 A g-1) simultaneously. The intrinsically safe Zn||I2 battery, one of the leading candidates aiming to replace traditional Pb-acid batteries, is still seriously suffering from short shelf and cycling lifespan, due to the uncontrolled I3--shuttling and dynamic parasitic reactions on Zn anodes. Considering the fact that almost all these detrimental processes terminate on the surfaces of Zn anodes, modifying Zn anodes' surface with protecting layers should be one of the most straightforward and thorough approaches to restrain these processes. Herein, a facile zeolite-based cation-exchange protecting layer is designed to comprehensively suppress the unfavored parasitic reactions on the Zn anodes. The negatively-charged cavities in the zeolite lattice provide highly accessible migration channels for Zn2+, while blocking anions and electrolyte from passing through. This low-cost cation-exchange protecting layer can simultaneously suppress self-discharge, anode corrosion/passivation, and Zn dendrite growth, awarding the Zn||I2 batteries with ultra-long cycle life (91.92% capacity retention after 5600 cycles at 2 A g-1), high coulombic efficiencies (99.76% in average) and large capacity (203-196 mAh g-1 at 0.2 A g-1). This work provides a highly affordable approach for the construction of high-performance Zn-I2 aqueous batteries.

Establishing High-Performance Quasi-Solid Zn/I2 Batteries with Alginate-Based Hydrogel Electrolytes.

Zinc-iodine (Zn/I2) batteries are recognized as a kind of leading candidate for large-scale energy storage systems, owing to the high-capacity dissolution-deposition reactions on both electrodes. Nevertheless, the lifespan of Zn/I2 batteries is severely limited by the uncontrolled shuttling of triiodide ions (I3-) and unfavorable side reactions on Zn anodes. Herein, an alginate-based polyanionic hydrogel electrolyte is designed and synthesized by ion exchange and Zn2+-induced cross-linking. The immobile, negatively charged polyanionic chains on the hydrogel skeleton effectively block I3- from shuttling, while simultaneously transporting cations that are indispensable for battery chemistry. Moreover, this hydrogel can also enhance the cycling durability of Zn anodes by alleviating Zn's dendritic growth and corrosion reactions, due to the homogenized Zn2+ flux and reduced interfacial contact between free water and metallic Zn. Consequently, this alginate-based hydrogel electrolyte enables stable Zn plating/stripping for over 600 h at 2 mA cm-2 and 2 mAh cm-2 (corresponding to 10% depth of discharge). Serving as an electrolyte for Zn/I2 full batteries, this hydrogel helps the battery to achieve a high capacity of 183.4 mAh g-1 (capacity retention = 97.6%) after even 200 cycles at 0.2 A g-1, 77.4% higher than that of the traditional ZnSO4 aqueous counterpart (residual capacity = 41.5 mAh g-1). This work indicates the promising potential of electrolyte design on the performance improvement of aqueous Zn/I2 batteries.