Intercalation of Li ⁺ vs Na ⁺ Ions in AlOOH Thin Films: Toward Low-Cost Solid-State Electrolytes

This study explores the influence of ionic incorporation via immersion in LiCl and NaCl on the structural, morphological, and electrochemical properties of AlOOH thin films synthesized by chemical bath deposition. X-ray diffraction reveals that LiCl treatment induces the formation of lithium carbonate and aluminum hydroxide phases, a transformation absent in NaCl-treated films, which retain the pristine AlOOH structure. Scanning electron microscopy shows pronounced nanoflake growth in LiCl-treated films, while NaCl exposure yields negligible morphological changes. X-ray photoelectron spectroscopy confirms the formation of surface carbonate species in LiCl-treated samples, suggesting enhanced CO₂ adsorption and conversion facilitated by Li⁺. Electrical characterization via current-voltage measurements indicates increased conductivity in LiCl-treated films due to Li⁺ mobility, contrasting with the resistive nature of NaCl-treated counterparts. Electrochemical impedance spectroscopy further supports these findings, revealing ionic diffusion behavior in LiCl-treated samples and limited ionic transport in the NaCl-treated films. These results highlight the unique role of Li⁺ in the modification of AlOOH thin films, yielding a room temperature ionic conductivity of 0.77 × 10^-4 S cm^-1, underscoring their potential for applications in ionic sensing, electrochemical storage, and gas capture technologies.