Ruiyong Chen,1,* Michael Knapp,2 Emad Maawad,3 Rolf Hempelmann1 1
Joint Electrochemistry Lab, KIST Europe/Saarland University, 66123 Saarbrücken, Germany 2 Institute for Applied Materials, Karlsruhe Institute of Technology, 76021 Karlsruhe, Germany 3 Institute of Materials Research, Helmholtz-Zentrum Geesthacht, 22607 Hamburg, Germany * E-mail:
[email protected],
[email protected]
A direct modification of the anion sublattice through fluorine incorporation/substitution in electrode materials has been proven to be an effective strategy to extend the composition space and to optimize performance due to the increased ionicity of the M−F bonds. We have recently reported the synthesis, structure (Fig. 1,2) and electrochemical properties (Fig. 3) of oxyfluoride/oxide with disordered rock-salt crystal structure (space group Fm-3m) [1-5].
Fig. 1 Li2VO2F with disordered rock-salt strucutre synthesized by ball-milling [1,2].
Fig. 2 Low lattice volume change for Li2VO2F upon 1.8 Li+ (de)intercalation [1,2]. Fig. 3 Performance of disordered rock-salt oxyfluorides [2-5].
Herein, we synthesize a rhombohedral VO2F (Fig. 4) and study the electrochemically driven structural change as cathode material for lithium batteries (Fig. 5). The theoretical capacity of VO2F is 526 mAh g-1 (compared to 442 mAh g-1 for V2O5) based on the assumed intercalation reaction: VO2F + xLi+ + xe- ↔ LixVO2F, supposing that x = 2 [6].
Fig. 4 Pristine VO2F: XRD, XANES and solid state 51V and 19F NMR.
Fig. 5 Electrochemical perfomance.
Similar to orthorhombic V2O5, structural phase transition into disordered rock-salt was observed for VO2F (Fig. 6), as confirmed by synchrotron X-ray diffraction and neutron diffraction.
Fig. 6 Structural transition into disordered rock-salt.
References 1. R. Chen, S. Ren, S. Indris, M. Fichtner, H. Hahn, Oxyfluoride compounds for lithium-cells and batteries, EP 14160894.3, 2014; WO 2015/140264 A1, 2015. 2. R. Chen, S. Ren, M. Knapp, D. Wang, R. Witter, M. Fichtner, H. Hahn, Disordered lithium-rich oxyfluoride as a stable host for enhanced Li+ intercalation storage, Adv. Energy Mater. 5 (2015) 1401814. 3. S. Ren, R. Chen, E. Maawad, O. Dolotko, A. Guda, V. Shapovalov, D. Wang, H. Hahn, M. Fichtner, Improved voltage and cycling for Li+ intercalation in high-capacity disordered oxyfluoride cathodes, Adv. Sci. 2 (2015) 1500128. 4. R. Chen, S. Ren, M. Yavuz, A. Guda, V. Shapovalov, R. Witter, M. Fichtner, H. Hahn, Li+ intercalation in isostructural Li2VO3 and Li2VO2F with O2- and mixed O2-/F- anions, Phys. Chem. Chem. Phys. 17 (2015) 17288. 5. R. Chen, S. Ren, X. Mu, E. Maawad, S. Zander, R. Hempelmann, H. Hahn, High-performance low temperature Li+ intercalation in disordered rock-salt Li-Cr-V oxyfluorides, ChemElectroChem 3 (2016) 892-895. 6. R. Chen, E. Maawad, S. Ren, M. Knapp, S. Zander, P. Beran, R. Hempelmann, Lithiation-driven structural transition of VO2F into disordered rock-salt LixVO2F, RSC Adv. 6 (2016) 65112-65118. Korea Institute of Science and Technology Europe Forschungsgesellschaft mbH Campus E7 1 66123 Saarbrücken Germany
Contact: Dr. Ruiyong Chen, E-mail:
[email protected]
