Wool/soy protein isolate membranes as separators toward more sustainable lithium-ion batteries

Abstract

Natural origin products exist in large quantities around the world and many times they are not properly exploited in order to realize their potential in novel applications, being often even discarded as by-products from other uses. In this study, wool and soy protein isolate (SPI) are proposed to develop separator membranes for lithium-ion batteries (LIBs), aiming toward a new generation of sustainable batteries. The developed membranes show suitable wettability by the electrolyte solution and are characterized by a porous morphology that becomes more irregular with the addition of wool with respect to the distribution and size of the pores. The physicochemical properties of the membranes are not strongly affected by the addition of wool, excepting for the low mechanical resistance of the SPI membranes, which is improved with the presence of wool. With respect to lithium-ion battery applications, the ionic conductivity is larger than 10−4 S.cm−1 and the lithium transference number ranges between 0.42 and 0.67, leading to excellent battery performance with a discharge capacity up to ~150 mAh.g−1 at C/10 rate. Overall, the developed membranes represent a suitable alternative to conventional LIB separators taking into account the need for environmental friendlier approaches compatible with a circular and sustainable economy.