Physical ionogels with only 2 wt % gelators as efficient quasi-solid-state electrolytes for lithium batteries

Abstract

Ionic liquid (IL)-based gel electrolytes (ionogels) show great potential as quasi-solid-state electrolytes (QSSEs) for lithium-ion batteries (LIBs). However, conventional ionogels face challenges involving complex gelation processes, high gelator content (usually greater than 20 wt %), lower conductivity than neat ILs, and low Li⁺ transference numbers. Here, we create novel lithium salt-containing supramolecular ionogels (SIGs) as efficient QSSEs for LIBs through a simple and environmentally friendly approach. By using a low-molecular-weight gelator, specifically 12-hydroxyoctadecanoic acid, lithium-containing IL electrolytes can be solidified at a gelator concentration of only 2 wt %. The resulting physical ionogels exhibit remarkable characteristics, including high ionic conductivity similar to neat ILs and improved electrochemical stability. In addition, these SIGs demonstrate a distinctive thermally reversible gel-to-sol transition, a quality not attainable in other QSSEs. This feature promotes better electrode/electrolyte contact, enabling excellent battery performance using LiFePO₄, LiNi_0.8Co_0.1Mn_0.1O₂, and LiCoO₂ cathodes, along with Li metal and Li₄Ti₅O₁₂ anodes.