Aromatic polyurea ion-solvating membranes for stabilized quasi-solid-state lithium metal batteries

Abstract

In Solid lithium metal batteries (LMBs), polymer electrolytes have been extensively studied due to their intrinsic safety and high energy density. However, commonly used polymer matrix such as polyethylene oxide (PEO), polyacrylonitrile (PAN), and polyvinylidene fluoride (PVDF) cannot solve the problem of lithium dendrites and low ionic conductivity, resulting in short battery life and low-capacity retention. Here, a series of aromatic polyurea ion-solvating membranes (ISMs) with rigid and flexible structures is designed and prepared. With incorporation of LiTFSI, these ISMs exhibit high ionic conductivity (1.81 × 10⁻³ S cm⁻¹), good electrochemical stability (5.1 V vs Li⁺/Li), and excellent mechanical strength (39 MPa). The formed inorganic/organic solid electrolyte interphase (SEI) layer enriched with LiF, Li₃N, and Li–N–C in the batteries leads to a uniform lithium deposition. As expected, the Li|Li symmetrical cells show a stable galvanostatic Li plating/stripping cycling performance with a low overpotential of 900 h at 0.1 mA cm⁻². Most importantly, the LFP|ISM|Li coin cells still have a high capacity of 142.9 mAh g⁻¹ after 650 cycles at 0.5 C, with a capacity retention rate of 91 %.