Comparison of the polymorphs of VOPO4 as multi-electron cathodes for rechargeable alkali-ion batteries
| Autor: | Yuh-Chieh Lin, Iek-Heng Chu, Shyue Ping Ong, Natasha A. Chernova, Marc Francis V. Hidalgo, M. Stanley Whittingham |
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| Rok vydání: | 2017 |
| Předmět: |
Renewable Energy
Sustainability and the Environment Chemistry Band gap Intercalation (chemistry) Kinetics Mineralogy 02 engineering and technology General Chemistry 010402 general chemistry 021001 nanoscience & nanotechnology Electrochemistry Alkali metal 01 natural sciences Redox 0104 chemical sciences Ion Physical chemistry General Materials Science Chemical stability 0210 nano-technology |
| Zdroj: | Journal of Materials Chemistry A. 5:17421-17431 |
| ISSN: | 2050-7496 2050-7488 |
| Popis: | Multi-electron polyanion cathodes offer the potential for achieving both high voltage and high capacity in rechargeable alkali-ion batteries. Among the few materials known to exhibit multi-electron cycling, the polymorphs of VOPO4, which operate on the V3+–V4+–V5+ redox couples, are particularly promising due to the high gravimetric capacities that have been achieved and the high voltage of the V4+/5+ couple. In this work, we performed a systematic first principles investigation, supported by careful electrochemical characterization and published experimental data, of the relative thermodynamic stability, voltage, band gap, and diffusion kinetics for alkali intercalation into the β, e and αI polymorphs of VOPO4. We find that all VOPO4 polymorphs remain reasonably stable with the insertion of one alkali ion per V, but are significantly destabilized with the insertion of two alkali ions per V. The voltages for Na insertion are ∼0.33–0.69 V lower than those for Li insertion. We find that the αI polymorph is predicted to have higher Li+ migration barriers and larger band gaps than the β and e polymorphs, which account for the relatively worse electrochemical cycling performance observed. On the other hand, only the αI polymorph exhibits reasonably low barriers for Na+ migration compared to the β and e polymorphs, which are consistent with observed electrochemical performances reported thus far in the literature. We also show that differences in the voltage, kinetics and rate capability of these different polymorphs for Li and Na insertion can be traced back to their fundamentally different VO6/VO5–PO4 frameworks. |
| Databáze: | OpenAIRE |
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