Many materials, such as minerals , clays , gels , gelatins , contain confined water in the structure. Fundamentally, confined water includes nano-confined water (also termed as crystallization water ) and nano-confined pseudo-water, which are HO species whose H:O stoichiometry is not 2:1, such as -OH group, hydroxide, and hydronium . In our previous study, we accidentally found the confined-water-containing Li1.25H1.63Ti2O5.44-σ has a lithium diffusion coefficient 3~5 orders of magnitude higher than the confined-water-free Li4Ti5O12-TiO2 . Such a discovery suggests that the Li-ion transport in oxide SEs can be enhanced by confined water in the crystal structure (Figure ). This work aims to test this hypothesis by studying how confined water affects the performance of Li-H-Ti-O quaternary compounds as SE. Li-H-Ti-O compounds with different amounts of confined water are first synthesized, then their Li ion conductivity and stability are characterized. Lastly, Li-ion batteries based on these compounds as SEs are made and the electrochemical performance is examined.