A Facile Surface Reconstruction Mechanism toward Better Electrochemical Performance of Li4Ti5O12 in Lithium-Ion Battery

' 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 (approximate to 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.