A highly flexible and adhesive polymer electrolyte with fast ion conduction prepared via UV-induced in-situ polymerization for lithium metal batteries

Cathode–electrolyte integration via in-situ polymerization is an effective strategy to reduce interfacial resistance in solid-state/quasi-solid-state lithium batteries ; however, ion conduction in the fraction of polymer electrolyte is still to be enhanced. Herein, we demonstrate a separator-free cathode–electrolyte integrated structure employing a novel poly(di(ethylene glycol) ethyl ether acrylate)-based quasi-solid polymer electrolyte (LiTFSI-poly(DEGA)-FEC QSPE, denoted as PDEGA-QSPE), prepared via UV-assisted in-situ polymerization. Poly(DEGA) as a linear polymer contains abundant ethylene oxide (EO) segments in its branched chain, exhibiting excellent flexibility and high adhesion. Benefited from the flexible molecular structure, PDEGA-QSPE exhibits a glass transition temperature ( T g ) as low as around −68 °C and a good room-temperature ionic conductivity of 2.3 × 10 −4  S cm −1 , and it also shows an oxidative potential up to 4.7 V. The LiFePO 4 |PDEGA-QSPE|Li battery possesses an initial capacity of 149.2 mAh g −1 and a capacity retention of 92.5 % after 300 cycles at 0.2 C under room temperature, and poly(DEGA)-based QSPE also has the potential to be applied to the high-voltage NCM811||Li battery. Compared with widely-employed monomers for in-situ polymerization such as poly(ethylene glycol) diacrylate (PEGDA), poly(DEGA) possesses remarkably improved flexibility and ion conduction capability, exhibiting broad research and application prospects.