Interfacially-enhanced quasi-solid electrolyte using ionic liquid for lithium-ion battery

•Quasi-solid electrolyte is fabricated facilely using LLZO, PVDF-HFP, and BMIM-TFSI.•Plasticizer effect of BMIM-TFSI increases the contact area between LLZO and PVDF-HFP.•Well-developed interface in electrolyte results in high Li-ion transference number.•QSE cell shows great performance and stable coulombic efficiency with LFP cathode. Solid-state electrolytes (SEs), promising alternatives to liquid electrolytes (LEs), have their own pros and cons, necessitating exploring combined systems to achieve optimal performance. However, several issues occur due to the poor interface between combined SEs. Herein, Li7La3Zr2O12 (LLZO) inorganic SE and PVDF-HFP (poly(vinylidene fluoride-co-hexafluoropropylene)) solid polymer electrolyte are combined with the ionic liquid BMIM-TFSI (1-Butyl-3-methylimidazoliumbis-(trifluoromethylsulfonyl)imide) to obtain quasi-solid electrolyte (QSE) via a facile method. This study reveals that BMIM-TFSI in PVDF-HFP acts as a plasticizer and has an important role in covering LLZO particles for the properly formed interface between inorganic SE particles and solid polymer electrolyte. Thanks to the well-built interface, the QSE exhibits a high Li-ion transference number (tLi+), good ionic conductivity, and outstanding cycling performance, including a high capacity of 140 mAh g− 1 and stable Coulombic efficiency. Therefore, QSE has high potential as a next-generation SE for lithium batteries with its good electrochemical properties and simple fabrication process. [Display omitted]