Traditional Li⁺ electrolytes often fail to meet the requirements for fast response due to their slower response speed. In this paper, we prepare five Li⁺/Al³⁺ composite electrolytes with varying Li⁺/Al³⁺ ratios to investigate their effects on the electrochromic properties of WO₃ thin films fabricated via magnetron sputtering. The results demonstrate that the coloring response time and memory effect of WO₃ films in Li⁺/Al³⁺ composite and pure Al³⁺ electrolytes significantly outperform those in pure Li⁺ electrolytes. Specifically, when the Li⁺/Al³⁺ ratio is 1∶3, the coloring response time is minimized at 1.05 s, and after 28 h under open-circuit conditions, the transmittance at 550 nm increases by only 7.1 percentage points. Moreover, the cycle stability of WO₃ films in composite electrolytes is markedly superior to that in pure electrolytes. Particularly at a Li⁺/Al³⁺ ratio of 1∶3, the WO₃ film exhibits optimal cyclic performance, with a charge retention rate of 90.38% after 1000 cycles of voltammetric cycling (CV) testing.

WO₃ films are deposited on indium tin oxide (ITO) substrates via DC reactive magnetron sputtering. Film thickness is measured using a BrukerDektakXT step profiler, and scanning electron microscopy (SEM) imaging is conducted with a Zeiss Sigma 500 at 15 kV. X-ray diffraction (XRD) analysis is performed using Philips X’Pert diffractometer with Cu Kα radiation to determine the crystalline structure of the films. Electrochemical properties are measured in a standard three-electrode setup using an Ag/AgCl reference electrode in various lithium perchlorate/aluminum perchlorate LiClO₄/Al(ClO₄)₃ electrolytes dissolved in propylene carbonate (PC). Chronoamperometry and cyclic voltammetry tests using a CHI760E electrochemical workstation are employed to evaluate response times and cyclic performance. Ultraviolet-visible (UV-Vis) spectrophotometry (Shimadzu UV-3600 plus) is used to characterize modulation rates.

Five groups of Li⁺/Al³⁺ composite electrolytes with different ratios are prepared, and their effects on the electrochromic performance of WO₃ film are studied. Key findings include: 1) The light modulation rate of WO₃ films in Li⁺/Al³⁺ composite electrolyte is higher than in pure Li⁺ electrolyte (Fig. 2). 2) Adding Al³⁺ to Li⁺ electrolytes significantly reduces the coloring response time, though the fading time gradually increases with higher Al³⁺ content (Fig. 3). 3) After 28 h under open-circuit conditions, the transmittance increase of WO₃ films in composite electrolytes (4 percentage points-9 percentage points) is similar to that in pure Al³⁺ electrolyte (8.4 percentage points) but significantly smaller than in pure Li⁺ electrolyte (Fig. 4). 4) With increasing Al³⁺ content, the Q_ex/Q_in ratio increases, achieving the highest stripping efficiency at a Li⁺/Al³⁺ ratio of 1∶3 (Fig. 5).

In this paper, we prepare WO₃ thin film via DC reactive magnetron sputtering, and the effects of different Li⁺/Al³⁺ ratios on their electrochromic properties are thoroughly investigated. XRD and SEM analysis reveal that WO₃ thin films are amorphous with a uniform, porous, and loose structure. Notably, incorporating Al³⁺ into Li⁺ composite electrolytes significantly reduces the coloring response time of WO₃ thin films, compared to pure Li⁺ electrolytes. Among the tested ratios, a Li⁺/Al³⁺ ratio of 3∶1 yields the best memory effect with the transmittance of the WO₃ thin film increasing by only 4.8 percentage points after 28 h under open-circuit conditions. Moreover, the WO₃ thin film demonstrates the shortest coloring response time (1.05 s) and superior cycle stability when the Li⁺/Al³⁺ ratio is 3∶1. At this ratio, the charge density reaches 21.08 mC/cm², and the charge retention rate remains as high as 90.38%. These findings confirm that introducing Al³⁺ into Li⁺ electrolytes enhances the electrochromic properties of WO₃ thin film. By optimizing the Li⁺/Al³⁺ ratio in the electrolyte solution, the electrochromic performance of WO₃ films can be effectively controlled, offering a promising approach for achieving a film with better functionality.