Powering Smart Windows: Unveiling Crystal Structure and Al-Ion Storage Correlation in WO3 Electrode Via XRD for Aqueous Al-Ion Battery with Real-Time Energy-Level Indication

Abstract

The potential for using aqueous-based electrochromic batteries in colour indicator energy storage devices, particularly energy-efficient buildings and wearable technology with visible energy level performance, is significant. Unfortunately, many materials that are able to change colour upon ion intercalation have low optical contrast and capacity. To address this, multivalent ions can be utilized, providing multiple electrons and thus increasing optical contrast and capacity. This work presents a novel Al-ion electrochromic battery with WO3 as the cathode material, Al metal as the anode and AlCl3 as the aqueous electrolyte. X-ray diffraction results demonstrate the high structural stability of the optimized WO3 film (~170 nm), which only experienced a 0.69 pm change during Al-ion intercalation and de-intercalation. A DC-EES device with two cathodes on either side of an Al metal film anode exhibited superior performance, with an open circuit potential of 1.2 V and a capacity of 200 mAh/m2 at 0.5 A/m2. Additionally, the device displayed excellent electrochromic behaviour upon discharge, achieving an optical contrast of ~70%. These results illustrate the promising potential of Al-ion electrochromic batteries as a cost-effective and safe option for applications such as smart windows and energy storage displays in modern infrastructures. Figure 1