A Novel Intercalation Cathode Material with 1.7 Li per Transition Metal

Vanadium-based materials have received considerable attention for lithium ion batteries due to the facts that vanadium is the fifth most abundant transition metal in the earth’s crust, its relatively low atomic mass, its multiple oxidation states. The redox operating voltage (typically < 4.5 V) of vanadium-based materials is typically within the stability limit of conventional electrolyte, and vanadium oxides have rich crystal structures [1]. The ability of layered V₂O₅ for Li⁺ insertion has been well characterized. Intercalation of one Li⁺ per formula unit corresponds to a specific capacity of 147 mAh g^-1. Further Li⁺ ions (x > 1 in Li_xV₂O₅) insertion may cause irreversible structural transformations [2].
In this work, a new high-capacity (> 400 mAh g^-1) and high energy density (> 1000 Wh kg^-1) cathode material comprising of lithium metal oxyfluoride with a representative composition of Li₂VO₂F has been synthesized through a mechanical ball-milling method. In comparison with the prior art, several remarkable features of this new compound Li₂VO₂F are (i) two-electron reaction based on V³⁺/V⁵⁺ is accessible per transition metal, (ii) the initial composition is at lithiated state, (iii) it has a high theoretical specific capacity of 462 mAh g^-1. Furthermore, in comparison with the start-of-the-art commercial cathode materials, this new material offers the opportunity to reach higher capacity and energy density.

References:

[1] N. A. Chernova, M. Roppolo, A. C. Dillon, M. S. Whittingham, J. Mater. Chem. 2009, 19, 2526
[2] C. Delmas, H. Cognac-Auradou, J. M. Cocciantelli, M. Ménétrier, J. P. Doumerc, Solid State Ion. 1994, 69, 257.