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Published January 14, 2014 | Supplemental Material + Published
Journal Article Open

Role of intermediate phase for stable cycling of Na_7V_4(P_2O_7)_4PO_4 in sodium ion battery


Sodium ion batteries offer promising opportunities in emerging utility grid applications because of the low cost of raw materials, yet low energy density and limited cycle life remain critical drawbacks in their electrochemical operations. Herein, we report a vanadium-based ortho-diphosphate, Na_7V_4(P_2O_7)_4PO_4, or VODP, that significantly reduces all these drawbacks. Indeed, VODP exhibits single-valued voltage plateaus at 3.88 V vs. Na/Na+ while retaining substantial capacity (>78%) over 1,000 cycles. Electronic structure calculations reveal that the remarkable single plateau and cycle life originate from an intermediate phase (a very shallow voltage step) that is similar both in the energy level and lattice parameters to those of fully intercalated and deintercalated states. We propose a theoretical scheme in which the reaction barrier that arises from lattice mismatches can be evaluated by using a simple energetic consideration, suggesting that the presence of intermediate phases is beneficial for cell kinetics by buffering the differences in lattice parameters between initial and final phases. We expect these insights into the role of intermediate phases found for VODP hold in general and thus provide a helpful guideline in the further understanding and design of battery materials.

Additional Information

© 2014 National Academy of Sciences. Contributed by William A. Goddard III, September 9, 2013 (sent for review July 21, 2013). This work was financially supported by National Research Foundation of Korea Grants NRF-2010-0029031 and NRF-2009-0094046 funded by the Korean Ministry of Science and Technology and Qatar National Research Fund NPRP 5-569-2-232. S.Y.L. acknowledges the National Research Foundation of Korea for the NRF-2013-Global PhD Fellowship Program. The generous computing time from the Korea Institute of Science and Technology Information is also gratefully acknowledged. Author contributions: S.Y.L., H.K., W.A.G., Y.J., and J.W.C. designed research; S.Y.L., H.K., J.C., J.H.L., B.G.K., J.-J.C., K.Y.C., W.C., S.-J.K., and J.W.C. performed research; S.Y.L., H.K., J.C., J.H.L., B.G.K., K.Y.C., W.C., S.-J.K., W.A.G., Y.J., and J.W.C. analyzed data; and S.Y.L., H.K., J.-J.C., W.A.G., Y.J., and J.W.C. wrote the paper.

Attached Files

Published - PNAS-2014-Lim-599-604.pdf

Supplemental Material - pnas.201316557SI.pdf


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