Lithium Salt Combining Fluoroethylene Carbonate Initiates Methyl Methacrylate Polymerization Enabling Dendrite-Free Solid-State Lithium Metal Battery

This work demonstrates a novel polymerization-derived polymer electrolyte consisting of methyl methacrylate, lithium bis(trifluoromethanesulfonyl)imide and fluoroethylene carbonate. The polymerization of MMA was initiated by the amino compounds following an anionic catalytic mechanism. LiTFSI plays both roles including the initiator and Li ion source in the polymer electrolyte. Normally, lithium bis(trifluoromethanesulfonyl)imide has difficulty in initiating the polymerization reaction of methyl methacrylate monomer, a very high concentration of lithium bis(trifluoromethanesulfonyl)imide is needed for initiating the polymerization. However, the fluoroethylene carbonate additive can work as a supporter to facilitate the degree of dissociation of lithium bis(trifluoromethanesulfonyl)imide and increase its initiator capacity due to the high dielectric constant. The as-prepared poly-methyl methacrylate-based polymer electrolyte has a high ionic conductivity (1.19 × 10⁻³ S cm⁻¹), a wide electrochemical stability window (5 V vs Li⁺/Li), and a high Li ion transference number ($t_{{\mathrm{Li}}^{+}}$) of 0.74 at room temperature (RT). Moreover, this polymerization-derived polymer electrolyte can effectively work as an artificial protective layer on Li metal anode, which enabled the Li symmetric cell to achieve a long-term cycling performance at 0.2 mAh cm⁻² for 2800 h. The LiFePO₄ battery with polymerization-derived polymer electrolyte-modified Li metal anode shows a capacity retention of 91.17% after 800 cycles at 0.5 C. This work provides a facile and accessible approach to manufacturing poly-methyl methacrylate-based polymerization-derived polymer electrolyte and shows great potential as an interphase in Li metal batteries.