Journal
NATURE ENERGY
Volume 5, Issue 10, Pages 777-785Publisher
NATURE PORTFOLIO
DOI: 10.1038/s41560-020-00697-2
Keywords
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Funding
- EPSRC
- SUPERGEN programme [EP/L019469/1]
- Henry Royce Institute for Advanced Materials [EP/R00661X/1, EP/S019367/1, EP/R010145/1]
- Faraday Institution [FIRG007, FIRG008]
- EPSRC [EP/K040375/1]
- EPSRC Tier-2 capital grant via the BATTDesign project [EP/P020259/1]
- EPSRC Tier-2 capital grant via AMAiB project [EP/P020259/1]
- BBSRC [PR140003]
- University of Warwick
- Birmingham Science City Advanced Materials Project 1 - Advantage West Midlands (AWM)
- Birmingham Science City Advanced Materials Project 2 - Advantage West Midlands (AWM)
- European Regional Development Fund (ERDF)
- EPSRC [EP/S019367/1, EP/S003053/1, EP/L019469/1, EP/R010145/1, 2285747, EP/K040375/1, EP/P020259/1] Funding Source: UKRI
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Li-rich cathode materials are potential candidates for next-generation Li-ion batteries. However, they exhibit a large voltage hysteresis on the first charge/discharge cycle, which involves a substantial (up to 1 V) loss of voltage and therefore energy density. For Na cathodes, for example Na-0.75[Li0.25Mn0.75]O-2, voltage hysteresis can be explained by the formation of molecular O(2)trapped in voids within the particles. Here we show that this is also the case for Li1.2Ni0.13Co0.13Mn0.54O2. Resonant inelastic X-ray scattering and(17)O magic angle spinning NMR spectroscopy show that molecular O-2, rather than O-2(2-), forms within the particles on the oxidation of O(2-)at 4.6 V versus Li+/Li on charge. These O(2)molecules are reduced back to O(2-)on discharge, but at the lower voltage of 3.75 V, which explains the voltage hysteresis in Li-rich cathodes.O-17 magic angle spinning NMR spectroscopy indicates a quantity of bulk O(2)consistent with the O-redox charge capacity minus the small quantity of O(2)loss from the surface. The implication is that O-2, trapped in the bulk and lost from the surface, can explain O-redox. Understanding the severe voltage hysteresis in the first cycle of Li-rich cathodes is essential to realize their full potential in batteries. P. G. Bruce and colleagues report the formation of molecular O(2)on charging rather than other oxidized O species is the cause for the voltage hysteresis.
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