Chemically Cross‐Linked Poly(2‐hydroxyethyl methacrylate)‐Supported Deep Eutectic Solvent Gel Electrolytes for Eco‐Friendly Supercapacitors

Abstract

Nonvolatile, ion‐dense electrolytes, such as ionic liquids and deep eutectic solvents (DESs) are attractive candidates for safe, high‐performance electrochemical/electrostatic energy storage devices. In this report, an inexpensive and eco‐friendly DES (1 : 2 mixture of choline chloride/ethylene glycol) has been incorporated into a solid‐state gel electrolyte using a chemically cross‐linked polymer scaffold formed through in situ UV copolymerization of 2‐hydroxyethyl methacrylate (HEMA) and poly(ethylene glycol) diacrylate. A high room‐temperature ionic conductivity of 5.7 mS cm−1 has been obtained for a DES gel containing 13.2 vol % polymer scaffold. Tunable DES gel compressive elastic modulus values, between 14 kPa and 1.0 MPa, could be obtained by varying the polymer content. Clear evidence of hydrogen‐bonding interactions between the poly(HEMA) scaffold and the DES anion was revealed through species self‐diffusivity measurements as well as by FTIR spectroscopy. Using a 22.9 vol % polymer‐supported DES gel as electrolyte/separator in a supercapacitor prototype with activated carbon fabric electrodes, a specific capacitance of 33.3 F g−1 and an energy density of 15.8 Wh kg−1 (based on the mass of two electrodes) were obtained during discharge at a current density of 0.01 A g−1. This work supports the notion that chemically cross‐linked polymer‐supported DES gel electrolytes are suitable for solid‐state, flexible supercapacitor applications.

Use of Deep Eutectic Solvents in Polymer Chemistry–A Review

“…Polymerization of monomers by DESs described in the literature are listed in Table 8. Quin and Panzer used in situ UV copolymerization of 2-hydroxyethyl methacrylate (HEMA) and poly(ethylene glycol) diacrylate in choline chloride/ethylene glycol to create a new class of gel electrolytes [77]. A DES gel containing 13.2 vol% polymer scaffold was obtained.…”

Supercapacitors in the Light of Solid Waste and Energy Management: A Review

“…[103][104][105][106][107][108][109][110][111][112][113][114][115][116][117][118][119] Gelated ubiquitous liquid electrolytes have also been successfully tested on supercapacitors to overcome risks in packaging, portability, and leakage. [109][110][111][112][113][114][115] Besides, to aid to their environment-friendly characteristic, several "green" materials such as egg white, [116] potato starch, [117,118] and rice starch, [119] processed through cost-effective strategies have been implemented as potential electrolytes in supercapacitors. Although recycling electrochemical devices is a common practice in many countries, supercapacitors are yet to gain attention in this regard.…”

A Poly(ionic liquid) Gel Electrolyte for Efficient all Solid Electrochemical Double-Layer Capacitor

“…This value is certainly lower than the acrylate gel based supercapacitor device prepared by Qin et al . 20 , where the electrolyte showed combination of robust elastic modulus (210 kPa) and reasonably high ionic conductivity (3.2 mS/cm). However, Pazner et al .…”