Lithium ion conducting PVdF-HFP composite gel electrolytes\ud based on N-methoxyethyl-N-methylpyrrolidinium\ud bis(trifluoromethanesulfonyl)-imide ionic liquid

摘要

Blends of PVdF-HFP and ionic liquids (ILs) are interesting for application as electrolytes in plastic Li\udbatteries. They combine the advantages of the gel polymer electrolytes (GPEs) swollen by conventional\udorganic liquid electrolytes with the nonflammability, and high thermal and electrochemical stability of\udILs.\udIn this work we prepared and characterized PVdF-HFP composite membranes swollen with a solution\udof LiTFSI in ether-functionalized pyrrolidinium-imide ionic liquid (PYRA12O1TFSI). The membranes were\udfilled in with two different types of silica: (i) mesoporous SiO2 (SBA-15) and (ii) a commercial nano-size\udone (HiSilTM T700). The ionic conductivity and the electrochemical properties of the gel electrolytes were\udstudied in terms of the nature of the filler.\udThe thermal and the transport properties of the composite membranes are similar. In particular, room\udtemperature ionic conductivities higher than 0.25mScm−1 are easily obtained at defined filler contents.\udHowever, the mesoporous filler guarantees higher lithium transference numbers, a more stable\udelectrochemical interface and better cycling performances. Contrary to the HiSilTM-based membrane,\udthe Li/LiFePO4 cells with PVdF-HFP/PYRA12O1TFSI–LiTFSI films containing 10 wt% of SBA-15 show good\udcharge/discharge capacity, columbic efficiency close to unity, and low capacity losses at medium C-rates\udduring 180 cycles.