Six-armed and dicationic polymeric ionic liquid for highly stretchable, nonflammable and notch-insensitive intrinsic self-healing solid-state polymer electrolyte for flexible and safe lithium batteries

Abstract

Solid-state polymer electrolytes (SPEs) with outstanding flexibility and self-healing capacity are appealing for utilization in reliable and wearable electronic devices. Herein, a highly stretchable (extensibility > 1500% and stress > 490 kPa), non-flammable and notch-insensitive intrinsic self-healing SPE based on six-armed poly(N,N,N-trimethyl-N-((2-(dimethylamino)ethyl methacrylate)-7-propyl)-ammonium dual bis(trifluoromethanesulfonyl) imides), imidazole-based ionic liquid (EMIM–TFSI) and LiTFSI is fabricated. The multi-armed structure in combination with the multiple charged center endow the six-armed dicationic polymeric ionic liquid (DPIL-6) with significantly strengthened ionic attractions and Van der Waals' force among the polymer segments, thus conferring the DPIL-6 derived SPE (DPIL-6-SPE) with prominent self-healing ability (recovery time < 2 h, 25 ℃). Moreover, DPIL-6-SPE presents a superior adhesion strength (weight loading > 200 g) towards lithium electrode, signifying excellent interfacial compatibility. Compared with the counterpart of monocationic polymeric ionic liquid derived SPE (MPIL-6-SPE), the multiple cationic center in DPIL-6-SPE facilitates the dissociation of lithium salt and liberates more Li+ from trapping with TFSI-, thereby resulting in a superior ionic conductivity (over 10-5 S cm−1 at room temperature) and lithium ion transference number (0.46). The as-assembled LiFePO4/DPIL-6-SPE/Li battery can deliver a high discharge capacity of 152.6 mAh g−1 at 0.1C, and its capacity retention rate reaches 94% after 50 cycles with a coulombic efficiency of 96%. In particular, the mechanical properties and conductivity of DPIL-6-SPE can fully recover after repeated damage, conferring the derived soft-pack battery stable powering capacity upon multi-angle bending and folding. The design of multi-armed and multiple charged PILs provides new avenues for developing flexible electronic devices with self-healing capacity.