Raman spectroscopic characterization and thickness assessment of hydrolysis in polymer-encapsulated Lithium hydride

Lithium hydride (LiH), known for its lightweight, high hydrogen storage capacity, and chemical stability, is poised to play a crucial role in various applications. These include neutron shielding in nuclear reactors, tritium breeding in fusion energy systems, and as a key component in low-carbon energy storage solutions. However, LiH's high reactivity with trace water leads to hydrolysis, generating products such as LiOH and Li₂CO₃ while releasing hydrogen gas, which severely limits its long-term storage and safety. Although encapsulation with low-permeability polymer films can delay hydrolysis, interfacial penetration of water molecules still induces gradual hydrolysis, resulting in material performance degradation. This study systematically investigates the hydrolysis behavior and mechanisms of polymer-encapsulated LiH using dual-wavelength near-infrared (NIR) Raman spectroscopy, a micro-confocal Raman spectrometer, and a wide-field Raman imaging system. Dual-wavelength NIR Raman spectroscopy successfully overcomes fluorescence interference from the polymer film, enabling non-destructive simultaneous detection of LiOH, Li₂CO₃, and LiOH·H₂O, with spatial mapping of hydrolysis products via characteristic peaks (e.g., 3665 cm^-1 for LiOH). A quantitative model correlating hydrolysis layer thickness with Raman signal intensity was established using CH stretching vibration (2930 cm^-1) of the polymer film as an internal standard, achieving high linearity. The hydrolysis layer primarily consists of LiOH, with LiOH·H₂O enriched near the polymer interface, and the process is governed by water vapor diffusion. This work provides a sensitive and non-destructive analytical approach for monitoring encapsulated LiH hydrolysis, offering critical insights for its long-term storage and performance evaluation.