Self-healable dynamic poly(urea-urethane) gel electrolyte for lithium batteries

Self-healing materials are actively studied in order to extend the lifetime and performance of batteries. Dynamic covalent networks have recently emerged as one of the best self-healable materials which allow thermosets to be reprocessed and recycled. Among all the different exchangeable bonds studied over the last few years, hindered urea bonds appear to be one of the most feasible options to create self-healable materials due to their exchange activation at low temperatures. Although this chemistry is very popular in composite and coating applications, it has not been considered for designing self-healable materials for batteries. In this work we synthesize a membrane containing dynamic hindered urea crosslinking points by reacting tris[2-(isopropylamino)ethyl]amine with hexamethylene diisocyanate, followed by the addition of polyethylene glycol. It is proved that this newly designed material possesses self-healable properties and higher ionic conductivity than the commercially available liquid electrolyte embedded in a porous Celgard® 2500 separator. The polyurethane gel electrolyte shows very homogeneous Li plating and stripping in Li symmetrical cells and is also compatible with Li-mediated electrochemical ammonia synthesis approaches. Most importantly, after severely mechanically damaging the gel membrane, the polymer electrolyte shows great recovery of the electrochemical properties, experiencing more than 100 charge/discharge cycles (after cutting) at C/5 rate.