In-situ UV cured deep eutectic solvent-based gel polymer electrolyte for Li metal batteries

Lithium metal batteries (LMBs) are a promising alternative to obtain high-performance and sustainable energy storage systems, overcoming the energy density limitations of current lithium-ion batteries. However, Li metal hinders their widespread implementation due to high chemical reactivity and dendritic growth, poor interfacial stability and safety concerns linked to the use of flammable liquid electrolytes. Gel polymer electrolytes (GPEs), incorporating non-flammable solvents, have emerged as viable solutions, combining mechanical stability with good electrochemical performance. In this work, a scalable and cheap in-situ fabrication process for a deep eutectic solvent (DES)-based GPE is presented, directly depositing and UV-crosslinking the precursor formulation on the cathode surface. The polyethylene glycol diacrylate-based polymeric matrix is cured in a lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and trifluoroacetamide (TFA)-based DES, with and without the addition of ethylene carbonate and diethyl carbonate mixture ( g -DES and g -DES10, respectively). Physico-chemical and electrochemical characterizations reveal weaker Li + coordination and improved transport properties and favourable interfacial properties in the presence of the carbonates. Li||LFP cells sporting g -DES10 GPEs exhibited good interfacial stability and stable cycling (163 mAh g −1 over 113 cycles) at room temperature and 1C, demonstrating the suitability of such production processes for scalable, safe and high-performance LMBs. • Non-flammable DES-based gel polymer electrolytes (GPEs) enhance safety and performance in lithium metal batteries (LMBs). • A scalable in-situ method is demonstrated by UV-curing the electrolyte precursor directly onto the cathode surface. • Addition of EC and DEC to g -DES GPE ( g -DES10) results in weaker Li + coordination and enhanced ionic transport. • The optimized GPE shows superior interfacial properties with lithium metal. • Li||LFP cells with g -DES10 GPE deliver stable cycling (163 mAh g -1 , 113 cycles at 1C), showing suitability for LMBs.