Novel Dilithium Metal Oxyfluoride As High Capacity Intercalation Cathode Material for Li-Ion Batteries

Lithium-ion batteries (LIBs) have transformed portable electronics and will play a key role in transport applications. However, the highest energy storage in the existing LIBs is insufficient for the long-term needs of society [1-2]. Good structural stability and minimal volume change over the entire operational Li insertion/extraction voltage range is preferable for LIBs to achieve good cell performance. The discovery and synthesis of new lithium intercalation materials with stable crystal structure and significantly improved energy density are urgently required.

Recently, we developed a new disordered dilithium metal oxyfluoride of Li₂VO₂F [3-4]. The novel material exhibits outstandingly high capacity of 420 mAh g^-1 with small lattice change of only 3% owing to its stable rock-salt host structure. Lithium, occupying 2/3 of the cation sites, is highly mobile [5-6]. Compared to the redox of V^3+/5+ at ~2.5 V, the chromium substitution into Li₂VO₂F leads to increased discharge voltages (accordingly higher energy density) and better cyclic stability. Moreover, nearly 1.8 Li⁺are accessible and can be reversibly stored at a current rate of ~ C/35 and room temperature [7]. Various characterization techniques were applied to verify the redox process and reversible structural change upon electrochemical cycling. The novel dilithium oxyfluoride intercalation material with disordered rock-salt structure opens new possibilities for obtaining higher storage capabilities for LIBs.

References:

1. P. G. Bruce, B. Scrosati, J.-M. Tarascon, Angew. Chem. Int. Ed., 2008, 47, 2930.
2. M. S. Whitthingham, Chem. Rev., 2004, 104, 4271.
3. R. Chen, S. Ren, S. Indris, M. Fichtner, H. Hahn, EP 14160894.3, 2014.
4. R. Chen, S. Ren, M. Knapp, D. Wang, R. Witter, M. Fichtner, H. Hahn, Adv. Energy Mater., 2015, DOI: 10.1002/aenm.201401814.
5. J. Lee, A. Urban, X. Li, D. Su, G. Hautier, G. Ceder, Science, 2014, 343, 519.
6. A. Urban, J. Lee and G. Ceder, Adv. Energy Mater., 2014, 4, 1400478.
7. S. Ren, R. Chen, E. Maawad, O. Dolotko, A. A. Guda, D. Wang, H. Hahn, M. Fichtner, to be submitted.