Synthesis And Electrochemical Performances Of Li_1+xVO₂as Anode Material For Lithium Ion Batteries

The Li-rich material Li1+xVO2(R-3m space group) is a novel low-voltage intercalation anode material which lithium can be reversibly intercalated into the layered structure (at-0.1V, only if x>0). The insertion composite compared with the commercial graphite has higher theoretical volumetric energy density because of the higher density (pLivo24.34vs. Pgraphite2.09g/cm3). Particularly, the electrochemical behaviors of Li1+x-VO2were largely affected by the content of the excess Li+.In this work, the pure Li1+xVO2with high capacity was prepared by solid state reaction methods with the optimized conditions. The facts such as precursor, atmosphere, the sintering temperature and time were selected to obtain the layered lithium rich oxides with excellent performance. Herein, we optimized the content of the excess Li by controlling the lithium and the vanadium ratios (Li/V) in the range from1.180to1.260by using the selected method. Highly crystallized hexagonal lithium vanadate Li1.20VO2was synthesized without any impurities, showing a superior specific discharge capacity of406mAh g"1between the cut off voltage of0.1-2.0V at a rate of0.1C. Nevertheless, the efficiency is only69.4%.The deterioration mechanisms for Li1.20VO2material were also investigated by ex-XRD, ex-XPS, cross section EDS&SEM and CV technologies at the various state of first discharge process and found that the excess Li is sufficient to promote a2-phase intercalation process between cubic close packed Li2VO2and hexagonal close packed Li1.20VO2at potentials of～0.1V. However, the process may be reversed on the charging (Li extraction).Carbon coating on the surface of Li1.20VO2material can improve the coulombic efficiency, cycling stability and rate characteristics. Different carbon sources were tried to coat at various contents. As a result, the malic acid at5%compared with the original material was showed the better performance, increasing the superior specific discharge capacity to501.5mAh g"1from406mAh g"1. Moreover, efficiency is also improved to73.6%.