Exploring SEI Characteristics in Propylene Carbonate-Based Electrolyte with 2-Isocyanatoethyl Methacrylate at Graphite Electrode

Propylene carbonate (PC) has the advantage of a much lower melting point than ethylene carbonate (EC), but it cannot suppress the exfoliation of graphite layers because of its cointercalation with Li⁺ before forming a stable solid electrolyte interface (SEI). This paper introduces 2−isocyanatoethyl methacrylate (ICEMA) as an additive in PC−based electrolytes. ICEMA is a bifunctional monomer in which the isocyanate group is linked by the ethyl group to the acrylate group, which reacts through thermal polymerization. The isocyanate moiety is initiated as a radical during the initial charging process to induce electropolymerization and reaction with the PC radical. Radicals propagate through the entire reaction at the electrode to form a stable SEI. The modified interface suppresses the cointercalation of Li⁺−PC to graphite electrode. In situ Fourier transform infrared effectively showed the polymerization of the isocyanate and active reaction with the PC radical. Consequently, the reaction mechanisms to form the stable SEI in PC−based electrolytes were determined.