Insights into the Charge Storage Mechanism of Li3VO4 Anode Materials for Li-Ion Batteries

Ball-milled Li3VO4 (LVO) offers higher practical specific charge values and better cycle stability than the pristine, mu m-scale material due to improved electronic conductivity within the electrode. Although the theoretical specific charge of LVO is estimated to be 592 mAh g(-1), its practical reversible specific charge retains 220 mAh g(-1) (1.12 Li+) on long-term cycling. At a very low rate of C/200 (=3 mA g(-1)), ball-milled Li3VO4-based anodes accomplish an almost full lithiation state of x=2.97 Li+ in Li3+xVO4. At the end of the first delithiation, the recovered LVO phase is able to only reversibly (de)lithiate about 1.8 Li+ in the following cycles. A careful investigation of the charge storage mechanism of LVO by operando X-ray diffraction revealed that the irreversible specific charge loss in the first cycle is mainly associated with an irreversible structural transformation via an intermediate phase on the first lithiation of LVO that leads to clear mechanistic differences in the reaction pathways between the first lithiation and delithiation.