Electrochemical Quantification of Lithium Oxide Impurity in Lithium Sulfide via Lithium–Sulfur Battery Operation

A novel electrochemical quantification method is proposed for determining low contents of lithium oxide (Li 2 O) impurities in lithium sulfide (Li 2 S), based on the operating principles of lithium–sulfur battery systems. Li 2 O is a critical impurity in Li 2 S used for next-generation battery applications, including sulfide solid-state electrolytes and high-energy cathodes. It promotes electrolyte decomposition and induces parasitic side reactions during solid electrolyte synthesis. In addition, due to its intrinsically low ionic and electronic conductivity, Li 2 O increases the overall electrode resistance. Accurate quantification of Li 2 O is therefore essential for achieving high-purity Li 2 S and a predictable performance. However, conventional techniques such as X-ray diffraction (XRD) and titration suffer from poor accuracy and reproducibility, especially at low concentrations or in amorphous forms. To address these challenges, we designed Li 2 S electrodes with controlled amounts of Li 2 O and employed linear sweep voltammetry (LSV) to detect and quantify the oxidation peak associated with Li 2 O around ∼3.7 V (vs Li/Li + ). A strong linear correlation ( R 2 > 0.992) was observed between the LSV peak area and Li 2 O content below 5 wt %. Cross-validation with industrial Li 2 S samples using XRD, SEM-EDS, and oxygen analysis further confirmed the reliability of this approach. This methodology enables direct quantification of a low Li 2 O content through a simple electrode fabrication and LSV measurement process. Its high accuracy, low cost, repeatability, and fast analysis speed make it a promising tool for the quality assessment of Li 2 S materials and process control in commercial production lines.