Economical, ecofriendly and easy to handle polymer-in-salt-electrolyte

Abstract

Polymer-In-Salt-Electrolytes (PISEs) are an emerging branch of polymer electrolytes which are supposed to address the shortcomings (slow ion movement due to polymer coupled motion and small cationic transference number) of Salt-In-Polymer-Electrolytes (SIPEs), but a PISE, which may be commercially used for fabrication of energy device is still a dream because of recrystallization and brittle matrix at higher salt concentration. Our group has developed a simple solution casting protocol for synthesis of an economical, eco-friendly and easy to handle PISEs from crosslinked starches, where there is no need of getting the molten state salt/salt-mixture. The thought process behind this protocol and selection of starch as host polymer is that the salt breaks the starch into smaller molecules resulting in generation new –OH and –H to interact with salt, i.e. increasing salt concentration itself creates a favorable atmosphere for its acceptance. Starch is hydrophilic in nature and presence of large amount of salt adds up to it, and such materials have moisture content varying from ∼5 % to 25 %, depending to salt and starch combination and concentration, which is a favorable property leading the synthesized PISEs to behave as Water-In-Polymer-Salt-Electrolytes (WiPSEs). By exposing the freshly synthesized samples to high humidity these materials were stabilized with respect to ambient humidity changes. These materials lead to ESR <10 Ω (reaching to as low as <1 Ω), wide electrochemical stability window (ESW > 2.5 V) and ion relaxation time is of the order of μSec. The supercapacitor fabricated using synthesized PISEs with commonly available supercapacitor electrodes have behavior at par with other electrolytes reported in the literature. With lab-synthesized activated carbons, a capacity of ∼125 F/g has been obtained with columbic efficiency >98 %. Since the synthesis protocol and chemicals used are economical, the starch-based PISEs are economical and also environment benign, because starch is a renewable polymer and the process uses only one extra chemical (methanol as solvent). The material is flexible and can be molded in the desired shape and size and hence is a potential candidate to reach at the commercial level, if explored in detail.