Solid State Ionics, Vol.332, 1-9, 2019
Improving the mechanical performance of green starch/glycerol/Li+ conductive films through cross-linking with Ca2+
This study uses calcium chloride to induce cross-linking of starch chains in order to enhance the mechanical response of starch-based solid electrolytes. The films are prepared at five different CaCl2 contents (0, 0.125, 0.250, 0.50, 1.0 g) using a fixed amount of glycerol (1.5 g), LiCl (1.5 g) and starch (3 g) dispersed in 100 g of water. X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR) and cyclic voltammetry are used to characterize the composites. An effective cross-linking of starch chains by calcium ions is revealed by FTIR, while the amorphous features of the film microstructure is exhibited by XRD. The estimated relative crystallinity in the absence of calcium is not higher than 6.5%, while the CaCl2 addition reduces this parameter as low as 3.0%. In connection with the above parameters, the ionic conductivity of calcium-free film is similar to 3.0 x 10(-5) S cm(-1), while it presents an increase with CaCl2 incorporation (similar to 7.0 x 10(-5) S cm(-1)) due to the presence of free Ca2+ remaining from the maximum cross-linking capacity. The electrical capacitance (similar to 0.032 mF.cm(-2)) is slightly affected by calcium-mediated cross-linking. However, the mechanical response is greatly improved as revealed by the elongation-at-break parameter, increasing from similar to 90% for calcium-free film to similar to 160% for films containing these ions. This indicates the enhancement of film elasticity, yielding 3D networks with robust mechanical stability.