Quasi-Solid-State Electrolytes: Enhancing the Future of Lithium-Ion Batteries

Abstract

Batteries are a cornerstone of the energy transition and the European Green Deal, enabling renewable energy integration and the decarbonization of transport and energy storage. However,safety concerns, such asthermal runaway from liquid electrolytes, and the energy density limitations of lithium-ion batteries present significant challenges. Solid-state electrolytes such as LLZO, LATP, and LAGP are promising alternatives, particularly when combined with energy-dense lithiummetal anodes, but they still exhibit lower ionic conductivity than conventional liquid electrolytes. To address this a non-flammable ionic liquid can be added to the solid-state electrolyte. Herein, the investigation of quasi-solid-state electrolytes comprising solidstate electrolytes, such as LLZO, LATP and LAGP infused with the ionic liquid Pyr₁₄FSI and LiTFSI salt is presented. This hybrid approach can significantly enhance the ion mobility and thus improving the ionic conductivity compared to the all-solid-state electrolytes. The study further examines fabrication methods for the solid-state electrolytes, focusing on pore formation using polymethyl methacrylate (PMMA) as a pore-forming agent in varying sizes and concentrations, and characterizing the resulting porosity via SEM and gas adsorption techniques. The ionic liquid is introduced into the porous structure using vacuum infiltration to ensure uniform distribution. Additionally, impedance spectroscopy and cyclic voltammetry are employed to investigate ion transport mechanisms and the structural compatibility between the ceramic framework and the ionic liquid. Our results highlight the improved ionic conductivity of quasi-solid-state systems relative to conventional liquid electrolytes and underline their potential as safer, high-performance alternatives for next-generation lithium-ion and lithium-metal batteries.