Recently, a layered lithium vanadium monodiphosphate Li₉V₃(P₂O₇)₃(PO₄)₂[LVPP] has been proposed as a promising cathode material for Li-ion batteries [1, 2, and 3]. Theoretically, extraction of maximum 6 Li ions per formula unit is possible [1, 3]. Thus a theoretical capacity of 173mAhg^-1 is achievable through complete oxidation of vanadium from its initial 3+ to 5+ state. Synthesis routes so far reported in literature require either H₂rich atmosphere during calcination or use expensive precursors that are air, moisture sensitive. 

Herein we report a low cost and easy two-step solid state synthesis approach to obtain pure LVPP.  A systematic study has been carried out to investigate the influence of crystallite size, carbon coating and working potential window on the specific discharge capacity of Li₉V₃(P₂O₇)₃(PO₄)₂ and  is discussed. LVPP, with crystallite size of 40nm and 4% carbon content facilitates the extraction of nearly 5 Li⁺ ions during the first charge cycle between 2.0-4.8V. Highly reversible specific discharge capacity of 115mAhg^-1 could be achieved in the same potential window. When the upper cut-off potential was reduced to 4.6V, a discharge capacity of 75mAhg^-1is obtained at charge /discharge rate of 1C.

This contribution presents a facile route to obtain a polyanionic framework material that utilizes more than one electron per transition metal. A much needed boost in capacity with improved cycling stability and rate capability can be achieved with proper tuning of the crystallite size and conductivity.

REFERENCES:

1)      Q.Kuang, J.Xu, Y. Zhao, X.Chen, L.Chen ElectrochimicaActa 56 (2011)  2201–2205

2)      M. Onoda And M. Inagaki  Journal Of The Physical Society Of Japan 80 (2011) 084801

3)      A. Jain, G. Hautier, C. Moore, B. Kang, J. Lee, H. Chen, N. Twu, and G. Ceder Journal of The Electrochemical Society, 159 (5) (2012) A622-A633

ACKNOWLEDMENTS:   This work was supported by the German Federal Ministry of Education and Research (BMBF) in the project Li-EcoSafe (03X4636A).