UV-cured self-healing gel polymer electrolyte toward safer room temperature lithium metal batteries

Solid polymer electrolytes are considered a useful solution for improving the safety of lithium metal batteries. However, these macromolecular systems show low ionic conductivity and suffer from limited cyclability at room temperature. In this work we propose the UV-induced, solvent-free radical copolymerization of poly(ethylene glycol) methyl ether methacrylate (PEGMEM, MW 500) and 2-(3-(6-methyl-4-oxo-1,4-dihydropyrimidin-2-yl)ureido)ethyl methacrylate (UpyMa) in the presence of poly(ethylene glycol) diacrylate (PEGDA, MW 575), used as crosslinker. The polymers, after activation in small amount of liquid electrolyte, show high thermal resistance, good lithium-ion conductivity and wide electrochemical window. Moreover, thanks to the quadruple hydrogen bond interaction of UpyMa dimer, the polymers show good self-healing properties both at 50 °C and room temperature. Such prepared polymers possess excellent interfacial stability and allow for stable lithium plating and stripping at room temperature. Last but not least, cycling tests against LFP cathode showed a fair and stable discharge capacity at 0.2C with 80% of capacity retention after 300 cycles. Most importantly, after severely mechanically damaging the electrolyte, it showed great recovery of the electrochemical properties, with a restored capacity of 115 mAh g⁻¹ at 0.2C and room temperature. This work highlights a promising strategy for safer room-temperature self-healing quasi solid-state lithium metal batteries.