Controlling Ionic Conductivity, Electrochemical Stability, and Interfacial Contact With Ionogel Electrolytes in Solid‐State Sodium‐Metal Batteries

Abstract

Sodium‐ion batteries are promising as a cost‐effective and sustainable alternative to lithium‐ion batteries because they rely less on critical raw materials. However, most sodium‐ion batteries use flammable liquid electrolytes. Replacing these with nonflammable solid‐like electrolytes can improve safety, reduce leakage, and increase energy density. Ionogels, which immobilize ionic liquid electrolytes within a solid matrix, are particularly attractive because they combine the advantages of ionic liquids, including high thermal stability, ionic conductivity, safety, and electrochemical stability, with the benefits of solid electrolytes. Despite these advantages, optimizing electrode–electrolyte interfacial contact remains a key but understudied challenge. This work examines how liquid loading and salt concentration affect the mechanical properties and interfacial contact of silica‐based ionogels. Increasing both parameters reduces the Young’s modulus to as low as 22 MPa while maintaining high ionic conductivity (4.3 mS cm −1 ). Higher salt concentrations improve compatibility with sodium metal and increase the critical current density to 0.5 mA cm −2 . NTP/Na cells using ionogels with the highest salt concentration (ILE_0.3) and an ionic liquid‐to‐silica ratio of 1.5:1 deliver 101  ±  4.6 mAh g −1 , comparable to cells containing a flammable liquid electrolyte (99  ±  0.4 mAh g −1 ).