Effects of lithium content on the electrochemical performance of Li_1+xV₃O₈ cathode materials for lithium-ion batteries

Lithium trivanadate (LiV3O8) is of great interest due to its large capacity, low cost and easy preparation. However, it still suffers from an inferior cyclability and rate capability. To solve these shortcomings of LiV3O8, a small extra amount of lithium was introduced into Li sites of LiV3O8. Herein, Li-doped LiV3O8 (Li1+xV3O8) materials were prepared and the electrochemical performance of Li1+xV3O8 changes with x from 0 to 0.1, 0.2 and 0.3. The discharge capacity of Li1+xV3O8 increases from x = 0 to 0.2 and then decreases, and the change trend of cycle performance is the same as that of discharge capacity. The optimal Li-doped LiV3O8 sample, Li1.2V3O8, exhibits much higher capacity and better cyclability and rate capability than LiV3O8. Galvanostatically discharged and charged between 2.0 and 4.0 V, Li1.2V3O8 and LiV3O8 present the initial discharge capacities of 305 and 268 mAh g(-1) at 0.1 C (30 mA g(-1)), respectively, and the corresponding capacity retentions are 87% and 80% after 50 cycles. Even at a high current rate of 2 C, Li1.2V3O8 exhibits high discharge capacity of 173 mAh g(-1), much higher than the discharge capacity of 133.6 mAh g(-1) for LiV3O8. The better electrochemical performance of Li1.2V3O8 can be ascribed to the doping of appropriate amount of Li+ in LiV3O8 and the resulted higher diffusion coefficients of Li+ in Li1.2V3O8.