Closing the\nLoop: Recyclable Solvate Ionic Liquids\nin Solid Polymer Electrolytes for Circular Economy

This\npaper demonstrates a pioneering method aimed at\nfurthering\nthe principles of a circular economy within energy storage systems.\nSpecifically, it focuses on the reclamation and recycling of solvate\nionic liquids (SILs), lithium in tetra-glyme (G4) with the TFSI/TFSA/NTf<sub>2</sub> (bis(trifluoromethanesulfonyl)imide) anion, from epoxy-based\nsolid polymer electrolytes (SPEs). The bicontinuous SPE matrix of\nG4:LiTFSI 7:3 epoxy resin is evaluated for its recyclability. The\napproach involves the extraction of SILs from SPEs and their subsequent\nreincorporation back into SPEs, thereby promoting a sustainable loop\nof resource utilization within the energy storage ecosystem. The recycling\nprocess, employing ethanol as an environmentally friendly solvent\nand basic physical separation (blending/shredding/comminution), yielded\na remarkable recovery rate of up to 92.8% SIL from the SPEs. The recycling\nprocess was repeated 5 times, with an average SIL recovery rate of\n83% (ranging from 92.8% to 81.1%), to demonstrate the robustness of\nthe process. Characterization studies, including nuclear magnetic\nresonance (NMR) spectroscopy, Fourier transform infrared (FT-IR) spectroscopy,\nthermogravimetric analysis (TGA), ionic conductivity, and flexural\ntesting, revealed that the properties of SPEs incorporating recycled\nSILs closely mirrored those of SPEs containing pristine SILs. Blended\nresin pulp was shown to be a promising filler for epoxy-based resin\nsystems. With 10% (w/w) filler, mechanical properties improved by\n11% for flexural modulus (1678 vs 1507 MPa) and 23% for flexural strength\n(35.8 vs 29.1 MPa) compared to the resin control, thereby demonstrating\nthe full recyclability of the SPE. These findings underscore the viability\nof SIL recycling, maintaining essential electrochemical and mechanical\nproperties that are crucial for energy storage applications. The implementation\nof the recycling process was calculated to result in a significant\ncost reduction of 66.51%, lowering the manufacturing cost of 1 kg\nof SPE from $1081.22 (USD) to $362.06 (USD) over five recycling cycles.\nOverall, the successful integration and recycling of SILs in SPEs\nrepresent a significant advancement toward closing the loop in energy\nstorage systems, fostering a more sustainable and circular approach\nto material utilization in the field of energy technology. This work\nrepresents the first report detailing both the yield and purity of\nan electrolyte recovered from an SPE, establishing a new benchmark\nfor transparency in reporting critical metrics in the field of energy\nstorage material recycling.