One-step synthesis of hexagonal TiOF2 as high rate electrode material for lithium-ion batteries: research on Li intercalation/de-intercalation mechanism

Abstract

Two novel nanocrystalline materials, hexagonal TiOF2 (hTiOF2, space group R3¯c hexagonal) nanocubes and LiTiOF2 (space group R3c hexagonal), were prepared by a one-step solvothermal method and the lithiation of hTiOF2 precursor, respectively. All the products have been characterized by means of X-ray diffraction, thermogravimetry, scanning electron microscopy, transmission electron microscope and high resolution transmission electron microscope. Furthermore, Rietveld analysis has been used to evaluate the structure of LiTiOF2. The electrochemical properties were evaluated using the products as cathode for half-cells in lithium-ion batteries (LIBs). It is confirmed that hTiOF2 and LiTiOF2 have the same frame and the Li intercalation/de-intercalation mechanism of hTiOF2 is discussed. An electrochemical activation process is confirmed in the charge-discharge cycles of hTiOF2 half-cells. The hTiOF2 half-cell after activation delivered a high specific capacity of 200mAh g−1 at 1C in the range of 3.0–0.8V and maintained a specific capacity of 120mAhg−1 at 20C over 1000 cycles, which is a very satisfying performance.