Through a facile sodium sulfide (Na₂S)-assisted hydrothermal treatment, clean and nondefective surfaces are constructed on micrometer-sized Li₄Ti₅O₁₂ particles. The remarkable improvement of surface quality shows a higher first cycle Coulombic efficiency (≈95%), a significantly enhanced cycling performance, and a better rate capability in electrochemical measurements. A combined study of Raman spectroscopy and inductive coupled plasma emission spectroscopy reveals that the evolution of Li₄Ti₅O₁₂ surface in a water-based hydrothermal environment is a hydrolysis–recrystallization process, which can introduce a new phase of anatase-TiO₂. While, with a small amount of Na₂S (0.004 mol L⁻¹ at least), the spinel-Li₄Ti₅O₁₂ phase is maintained without a second phase. During this process, the alkaline environment created by Na₂S and the surface adsorption of the sulfur-containing group (HS⁻ or S²⁻) can suppress the recrystallization of anatase-TiO₂ and renew the particle surfaces. This finding gives a better understanding of the surface–property relationship on Li₄Ti₅O₁₂ and guidance on preparation and modification of electrode material other than coating or doping.