| Autor: |
Britto, Sylvia, Seymour, Ieuan, Halat, David, Hidalgo, Marc FV, Siu, Carrie, Reeves, Philip, Zhou, Hui, Chernova, Natalya A, Whittingham, Stanley, Grey, Clare |
| Přispěvatelé: |
Reeves, Philip [0000-0003-4339-7282], Grey, Clare [0000-0001-5572-192X], Apollo - University of Cambridge Repository |
| Rok vydání: |
2020 |
| Předmět: |
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| DOI: |
10.17863/cam.50007 |
| Popis: |
The lithium ion battery cathode material β-VOPO4 is capable of intercalating more than one Li ion per transition metal ion due to the accessibility of both the V5+/V4+ and V4+/V3+ redox couples at ~4.5 V and ~2.3 V vs. Li, respectively, giving a theoretical capacity greater than ~300 mAh g−1. The ability to perform full and reversible two Li-ion intercalation in this material, however, has been a matter of debate and the poor crystallinity of the fully lithiated phase has thus far precluded its complete structural characterization by conventional diffraction-based methods. In this work, 7Li and 31P NMR spectroscopy, in combination with first principles DFT calculations, indicate that chemical lithiation results in a single phase β-Li2VOPO4 exhibiting a complex Li ordering scheme with lithium ions occupying multiple disordered environments. 2D NMR 7Li correlation experiments were used to deduce the most likely Li ordering for the β-Li2VOPO4 phase from amongst several DFT optimised structures. In contrast, electrochemically lithiated β-Li2-xVOPO4 discharged to 1.6 V exhibits, in addition to β-Li2VOPO4, a β-Li1.5VOPO4 phase. The existence of β-Li1.5VOPO4 is not reflected in the flat galvanostatic charge and discharge curves nor is evident from diffraction-based methods due to the very close structural similarity between the β-Li1.5VOPO4 phase and β-Li2VOPO4 phases. We demonstrate that solid state NMR spectroscopy, in combination with DFT results provides a powerful tool for identifying intermediate states formed during charge/discharge of these complex phosphates as these phases can be distinguished from the end member phases primarily by the nature of the lithium ordering. |
| Databáze: |
OpenAIRE |
| Externí odkaz: |
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