In-situ crosslinked single ion gel polymer electrolyte with superior performances for lithium metal batteries

Abstract

Conventional dual-ion conductive gel polymer electrolytes (GPEs) attracted tremendous interest for their combined advantages of liquid and solid electrolytes. However, their cycling performance usually degrades due to the concentration polarization of anions. Single lithium ion gel polymer electrolytes (SLIGPEs), which have anions covalently bonded to the polymer or inorganic backbone, can suppress the motion of anions by the interactions between the pedant anions and mobile ions. Especially, Li+ deposition in SLIGPEs can be regulated uniformly to avoid lithium dendrite growth. Herein, novel 3D-structured SLIGPEs were prepared by in-situ crosslinking of lithium (4-styrenesulfonyl) (trifluoromethanesulfonyl) imide (LiSTFSI) with polyethylene glycol dimethacrylate (PEGDMA), soaked with liquid electrolyte. The obtained SLIGPEs not only promote the absorption of liquid electrolyte and accelerate the transport of Li+, but also show a high limitation for the migration of anions, proved by high ionic conductivity (2.74 × 10−5 S cm−1 at room temperature) and high lithium ion transference number (0.622) of SLIGPE-3.5, respectively. The long cycle life (cycling for over 600 h under 0.05 mA cm−2 and 0.1 mA cm−2) of symmetric lithium batteries with SLIGPEs as both separator and electrolyte exhibits good interfacial stability between SLIGPEs and electrodes. Meanwhile, LiFePO4/SLIGPE-2/Li shows a specific discharge capacity of 132.1 mAh g−1 at 0.1 C, 80.0% of the capacity retention ratio and 99.0% of the coulombic efficiency after 150 cycles at room temperature. Moreover, confirmed by SEM, lithium dendrite growth is significantly suppressed during repeated Li plating/stripping cycles. Density functional theory calculations (DFT) confirm the mutual interactions between STFSI− pendants and ions in electrolytes and that between PEO segments and ions. We believe that these in-situ SLIGPEs with superior performances have great potential for the application in lithium metal batteries.