Paper-Supported Sodium Alginate Composite Separator Prepared by Polymer-Assisted Phase Separation for Lithium Ion Batteries

Ecofriendly and renewable properties are highly desirable for separators of lithium batteries, apart from the notorious safety issues. As a natural polysaccharide material, sodium alginate (SA) has outstanding biodegradability and biocompatibility and has usually been used for the binder of electrodes due to its high ionic conductivity. Herein, SA porous separators were initially prepared by a facile polymer-assisted phase separation in which polyethylene glycol (PEG) and acetonitrile acted as a pore-forming agent and an extraction solvent, respectively. The influence of PEG content on the pore formation was systematically investigated, and the uniform and continuous pore structures were successfully realized at the PEG content of 200–500 wt %. Additionally, the cellulose-based paper support (KP) and poly(vinylidene fluoride-co-hexafluoropropylene) porous coating (PVH) were adopted for the decent mechanical integrity of SA porous membranes. The prepared SA composite separators showed excellent thermal dimensional stability, high porosity, and good electrolyte wettability. Moreover, the polar features of SA endowed the composite separators with high ionic conductivity (4.8 mS cm^–1) and lithium ion transference number (0.62). The strong depression capacity of lithium dendrites and a comparable electrochemical performance were also observed for the SA-based separators compared with the pure KP and commercial polyolefin separators.