High pseudocapacitive lithium-storage behaviors of amorphous titanium oxides with titanium vacancies and open channels

Amorphous titanium oxides have emerged as potential substitutable anode materials for high-rate lithium-ion batteries with the merits of abundant lithiation sites and accessible short ion diffusion channels. However, extreme differences in electrochemical properties and a poor understanding of the structure-property relationship for amorphous titanium oxides prepared via various synthetic strategies, hinder their further application. We designed amorphous titanium oxides with a unique structure and provided a moderate understanding of how titanium vacancies /open pore channels affect lithium ions (Li+) transportation behaviors in the amorphous titanium oxides. Galvanostatic charge/discharge curves and cyclic voltammetry (CV) tests revealed that two-step pseudo-capacitive behaviors, different from the diffusion-controlled process in anatase TiO2, mainly control Li+ insertion/extraction capacity in amorphous titanium oxides. Surface chemistry and structure analysis with FTIR and 1H solid-state NMR reveal that amorphous titanium oxides are rich in protons bonded to bridging hydroxyl groups. Density functional theory (DFT) calculations imply that the titanium vacancies and open channels promote lithium insertion/de-insertion processes with the two-step storage behaviors, favoring the pseudo-capacitive type in the amorphous titanium oxides. Our study may provide greater insight into the lithiation behaviors in amorphous materials and helpful guidelines in designing other high-capacity amorphous-oxide electrode materials for alkali-ion batteries.