## 3 Results and Discussion
### Electrochromic Switching Characteristics
For the films calcined at 350 \({}^{\circ}\)C, \(D_{\text{a,CV}}\) was found in the same order of magnitude as for WO31 comp calcined at 250 \({}^{\circ}\)C (Table 7) and also the values of \(\Delta T_{\text{710 nm}}\) and \(\Delta CE_{\text{710 nm}}\) lie in the range of the upper limit of the obtained values for the films annealed at 250 \({}^{\circ}\)C (Table 8). These observations confirm facile diffusion of Li\({}^{+}\) in amorphous WO3 that by GIXRD was observed to persist up to 350 \({}^{\circ}\)C (Figures 2 and S2). After calcination at \(T\geq 450\)\({}^{\circ}\)C, the values of \(\Delta T_{\text{710 nm}}\) and _CE_710 nm decreased and were found close to the lower limit of the values for the films calcined at 250 \({}^{\circ}\)C and a drastic change can be clearly seen for the effective diffusion coefficients, which are up to two orders of magnitude smaller than \(D_{\text{a,CV}}\) determined after annealing at 250 \({}^{\circ}\)C. Slow diffusion in crystalline films formed after calcination at \(T\geq 400\)\({}^{\circ}\)C (GIXRD, Figures 2 and S2) confirmed the disadvantage of a crystalline film structure for electrochromic performance as observed earlier [14,61,62]. However, the direct comparison of WO31 comp films fabricated without additives with WO31 up600 prepared with PEG 600 as additive (Table S1) shows a benefit of a microporous starting structure even for a crystalline film resulting in a more facile diffusion of ions. \begin{table}
\begin{tabular}{l c c c c c c} \hline \hline \multirow{2}{*}{**Film Type**} & \multicolumn{2}{c}{\(\Delta T_{\text{710 nm}}\)/\%} & \multicolumn{2}{c}{**x**} & \multicolumn{2}{c}{_CE_710 nm/cm\({}^{2}\) C\({}^{-1}\)} \\  & **CV** & **CA** & **CV** & **CA** & **CV** & **CA** \\ \hline WO31 comp & 28.8 \(\pm\) 8.4 & 25.4 \(\pm\) 2.7 & 0.37 \(\pm\) 0.07 & 0.38 \(\pm\) 0.05 & 53.2 \(\pm\) 12.6 & 34.5 \(\pm\) 5.9 \\ WO31 up400 & 68.2 \(\pm\) 3.5 & 63.5 \(\pm\) 1.7 & 0.43 \(\pm\) 0.04 & 0.53 \(\pm\) 0.08 & 75.4 \(\pm\) 3.9 & 58.6 \(\pm\) 5.6 \\ WO31 up600 & 70.0 \(\pm\) 4.3 & 64.2 \(\pm\) 6.6 & 0.41 \(\pm\) 0.05 & 0.57 \(\pm\) 0.05 & 74.5 \(\pm\) 7.9 & 54.3 \(\pm\) 8.8 \\ WO31 mp & 31.5 \(\pm\) 1.8 & 40.8 \(\pm\) 3.3 & 0.31 \(\pm\) 0.06 & 0.45 \(\pm\) 0.05 & 67.7 \(\pm\) 4.9 & 40.7 \(\pm\) 1.6 \\ WO31 up7 & 75.3 \(\pm\) 2.0 & 75.7 \(\pm\) 0.2 & 0.44 \(\pm\) 0.10 & 0.68 \(\pm\) 0.04 & 85.2 \(\pm\) 5.2 & 65.0 \(\pm\) 4.2 \\ commWO3 & 59.6 & 88.5 & 0.32 & 0.45 & 68.3 & 67.1 \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Mean values and standard deviation of the transmittance modulation \(\Delta T_{\text{710 nm}}\), the Li\({}^{+}\) content \(x\) in Li\({}_{x}\)WO3 and the coloration efficiency _CE_710 nm obtained from CV at a scan rate of 5 mV s\({}^{-1}\) or from CA measurements. As shown in Figure 1, the WO\({}_{3\,|}\)up400, WO\({}_{3\,|}\)up600 and WO\({}_{3\,|}\)up films were thicker than the films prepared without additives. Therefore, to check if the observed improvement of the transmittance modulation over WO\({}_{3\,|}\)comp was provided by such increased thickness of the films and to directly compare the performance to commWO\({}_{3}\), thicker films of WO\({}_{3\,|}\)comp, WO\({}_{3\,|}\)up600 and WO\({}_{3\,|}\)upup with similar thickness were prepared by subsequent preparation of several films onto each other. The thicker films (Figure 8) changed into an almost as deep blue as commWO\({}_{3}\) at, however, even slightly improved transparency in the bleached state (Figure S11d). Despite deep initial coloration, a reversible \(\Delta T_{710\mathrm{nm}}\) (Figure 8) of just 0.35% was measured for a 646 nm thick WO\({}_{3\,|}\)comp film allowing a reversible change between 0.76% and 0.41% only, indicating heavily trapped ions after the initial coloration step.