Electrochemically Induced Sol-Gel Deposition of Solid Electrolyte Thin Films for Li-Ion Batteries

Abstract

Electrochemically induced sol-gel deposition is a powerful method for synthesizing oxide and composite thin films directly onto conductive substrates. By applying cathodic currents, OH- ions are locally generated, triggering rapid gelation near the electrode surface. This technique has previously enabled the formation of mesoporous silica films using surfactant templates. Here, the method is extended to incorporate an ionic liquid electrolyte (ILE) as the templating agent, enabling direct electrodeposition of ILE-silica composite electrolytes. These nanocomposites combine the mechanical stability of silica with the high ionic conductivity of ILEs. Unlike conventional sol-gel approaches requiring days for solidification, this electrochemical process enables film growth within minutes, with tunable thicknesses (1–34 μm). The deposited layers were characterized by scanning electron microscopy, Raman, and Fourier-transform infrared spectroscopy, and integrated into all-solid-state thin-film test cells using TiO2, LiMn2O4 (LMO), and LiNi0.5Mn1.5O4 (LNMO) cathodes with lithium metal anodes. TiO2-based cells showed excellent compatibility and stable cycling over 75 cycles. For L(N)MO cells, a pre-lithiation step was required to prevent cathode degradation. Ionic conductivities of 0.1–0.5 mS cm−1 were measured. This work demonstrates a fast, scalable, and versatile approach for integrating solid electrolytes directly onto battery electrodes, bridging the gap between liquid-based processing and solid-state battery performance.