Lithium salt combining fluoroethylene carbonate initiates MMA polymerization enabling dendrite-free solid-state lithium metal battery

This work demonstrates a novel polymerization-derived polymer electrolyte (PDPE) consisting of methyl methacrylate (MMA), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) or lithium bis(fluorosulfonyl)imide (LiFSI) and fluoroethylene carbonate (FEC). The polymerization of MMA was initiated by the amino compounds following an anionic catalytic mechanism. It is worth noting that LiTFSI plays both roles including the initiator and lithium-ion source in PDPE. In principle, LiTFSI has great difficulty in initiating the polymerization reaction of MMA monomer. However, FEC additive can work as a supporter to facilitate the degree of dissociation of LiTFSI and increase its initiator capacity due to the high dielectric constant. The as-prepared PDPE 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 transfer number (tLi+) of 0.74 at room temperature (RT). Moreover, this PDPE can effectively work as an artificial protective layer on Li metal anode surface, which enabled the symmetric Li symmetric cell to achieve a long-term cycling performance at 0.2 mAh cm-2 for 2800 h. The LiFePO4 battery with PDPE modified lithium 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 MMA-based PDPE and shows great potential as an interphase in SSLMBs.