This study explores the potential of titanium disulfide (TiS₂) as an active material for aqueous calcium-ion batteries (CIBs). We investigate the electrochemical redox reactions of calcium ions within TiS₂ and assess its suitability for use in aqueous CIBs. Additionally, we examine the impact of varying electrolyte concentrations, ranging from 1.0 to 8.0 mol dm⁻³, on TiS₂ electrode reactions. Our findings reveal that TiS₂ exhibits distinct charge–discharge behaviors in various aqueous calcium-ion electrolytes. Notably, at higher electrolyte concentrations, TiS₂ effectively suppresses the hydrogen generation reaction caused by water decomposition. In situ X-ray diffraction analysis confirms the intercalation of Ca²⁺ ions between the TiS₂ layers during charging, which is a groundbreaking discovery, signifying TiS₂’s applicability in aqueous CIBs. X-ray photoelectron spectroscopy analysis further supports the formation of a solid electrolyte interphase (SEI) on the TiS₂ electrode surface, contributing to the suppression of electrolyte decomposition reactions. Furthermore, we investigate the influence of anions in the electrolyte on charge–discharge behavior. Our findings suggest that the choice of anion coordinated with Ca²⁺ ions affects the SEI formation and cycling performance. Understanding the role of anions in SEI formation is crucial for optimizing aqueous CIBs. In conclusion, this research underscores TiS₂’s potential as an active material for aqueous calcium-ion batteries and emphasizes the importance of the electrolyte composition in influencing SEI formation and battery performance, contributing to sustainable and efficient energy storage technologies.

This study explores the potential of titanium disulfide (TiS2) as an active material for aqueous calcium-ion batteries (CIBs). We investigate the electrochemical redox reactions of calcium ions within TiS2 and assess its suitability for use in aqueous CIBs. Additionally, we examine the im-pact of different electrolyte concentrations on TiS2 electrode reactions. Our findings reveal that TiS2 exhibits distinct charge-discharge behaviors in various aqueous calcium-ion electrolytes. Notably, at higher electrolyte concentrations, TiS2 effectively suppresses the hydrogen genera-tion reaction caused by water decomposition, demonstrating its potential as an active material for aqueous CIBs. In-situ X-ray diffraction analysis confirms the intercalation of Ca2+ ions be-tween TiS2 layers during charging. This confirmation is groundbreaking, as it represents the first experimental evidence of calcium ions being electrochemically inserted between TiS2 layers from aqueous solutions, signifying a previously unreported achievement and strongly suggesting TiS2's applicability in aqueous CIBs. X-ray photoelectron spectroscopy analysis further supports the formation of a solid electrolyte interphase (SEI) on the TiS2 electrode surface, contributing to the suppression of electrolyte decomposition reactions. Furthermore, we investigate the influ-ence of anions in the electrolyte on charge-discharge behavior. Our findings suggest that the choice of anion coordinated with Ca2+ ions affects SEI formation and cycling performance. Un-derstanding the role of anions in SEI formation is crucial for optimizing aqueous CIBs. In con-clusion, this research underscores TiS2's potential as an active material for aqueous calcium-ion batteries and emphasizes the importance of electrolyte composition in influencing SEI formation and battery performance. These findings contribute to the development of more sustainable and efficient energy storage technologies.