Application of experimental design to the conductivity optimization for waterborne polyurethane electrolytes

The optimization of conductivity for waterborne polyurethane (WPU) electrolytes and liquid electrolytes was studied by using response surface methodology (RSM) coupled with central composition design (CCD). Alternating current impedance and differential scanning calorimeter experiments were performed to obtain the ionic conductivities and thermal properties of WPU electrolytes, respectively. By means of RSM and CCD, the effect of lithium perchlorate (LiClO4) concentration and ratio of propylene carbonate (PC) to ethylene carbonate on conductivity for WPU electrolytes has been systematically investigated. Through this methodology, an empirical equation of conductivity for WPU electrolytes is obtained via regression analysis to be plotted as contour diagrams, facilitating the straight examination of experimental results. The contour plots show that the maximum conductivity (ca. 0.22 mS cm(-1)) can be obtained at a LiClO4 concentration of 0.9 M and a PC content of 37.5%. To confirm this optimum, three additional experiments were performed and the average conductivity at room temperature is 0.282 mS cm(-1).