High-Performance Aqueous Electrochromic Battery for Smart Window Application: Mechanistic Insights of Al-Ion (De)Intercalation Kinetics in Thickness-Optimized WO₃

Abstract

Aqueous-based electrochromic batteries have significant potential for use in color indicator energy storage, including energy-efficient buildings and wearable devices with visible energy level performance. While many materials have the ability to change color upon ion intercalation, they often have low optical contrasts and capacities. To address these issues, multivalent ions can provide a solution by providing multiple electrons, resulting in a higher optical contrast and capacity. Herein, we propose an Al-ion electrochromic battery with a unique design, utilizing WO 3 as the cathode material, Al metal as the anode, and AlCl 3 as the aqueous electrolyte. Ex situ X-ray diffraction results reveal that the peak position and interlayer spacing of the optimized WO 3 porous thin film (∼170 nm) change during Al-ion intercalation and deintercalation, indicating the high structural stability of the optimized WO 3 electrode. A double cathode-electrochromic battery (DC-EES) device consisting of two cathodes on either side of an Al metal film anode was fabricated and demonstrated superior electrochemical performance due to its increased active surface area and open circuit potential. The device exhibited an open circuit potential of ∼1.2 V and a capacity of ∼155 mAh/ m 2 at 0.5 A/m 2 , which are sufficient values for powering an electronic device. Additionally, the developed device exhibited excellent electrochromic behavior upon discharge with an optical contrast of 68% (transparent and blue). These results show the great potential of Al-ion electrochromic batteries as a cost-effective and high-safety material for applications in smart windows and energy storage displays in modern infrastructures.

Electrochromic and Energy Storage Performance Enhancement by Introducing Jahn–Teller Distortion: Experimental and Theoretical Study

“…Zn foil was purchased from ThermoFisher. Following a previous work from the laboratory, tin-doped indium oxide (ITO) was deposited using DC magnetron sputtering …”

“…Following a previous work from the laboratory, tin-doped indium oxide (ITO) was deposited using DC magnetron sputtering. 16 Synthesis of HWO and AWO. HWO (WO 3 •H 2 O) particles were synthesized by a hydrothermal method using sodium tungstate (Na 2 WO 4 •2H 2 O) as the precursor.…”

“…In this context, aqueous electrolyte-based rechargeable batteries (ARBs) have appeared to be very promising compared to their organic counterparts due to advantages, such as nontoxicity, low cost, nonflammability, and high ionic conductivity, the latter being important toward the high-power density of the device . Recently, many efforts have been made to optimize the energy storage mechanism while aiming for high optical modulation. − Traditional electrochromic batteries based on Li + , Na + , or K + ions suffer from inherent issues, such as relatively low power density, due to their monovalent nature and high reactivity. − Given these shortcomings, multivalent ions, such as Zn 2+ , Al 3+ , and Ca 2+ , have been explored. − Among various multivalent ARBs, zinc-ion-based batteries show superior performance due to a low redox potential (−0.76 V vs SHE), abundance, and high volumetric capacity (5855 mAh/cm 3 ). − Furthermore, the size of Zn 2+ ions is comparable to that of Li + ions, offering advantages for ion intercalation. Elezzabi et al demonstrated the initial utilization of Zn 2+ -ion intercalation in an electrochromic battery incorporating 1 M ZnSO 4 .…”

Complementary electrochromic device via a scalable solution process: a step towards affordable and energy-efficient smart windows

“…ECDs have garnered significant interest for their ability to offer user-controlled light transmission, presenting a viable solution to the challenge of balancing energy efficiency and user comfort. [3][4][5][6][7][8] A standard structure of ECD consists of four layers where an electrolyte is sandwiched between a bare transparent conducting electrode (TCE) and a TCE hosting an electrochromic (EC) film. A variant of this design, the complementary ECD (CECD) involves an extra EC layer on the bare TCE to enhance the optical contrast via a complementary coloration mechanism.…”