First cycle voltage hysteresis in Li-rich 3d cathodes associated with molecular O2 trapped in the bulk

Journal article

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 Na0.75[Li0.25Mn0.75]O2, voltage hysteresis can be explained by the formation of molecular O2 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 17O magic angle spinning NMR spectroscopy show that molecular O2, rather than O22−, forms within the particles on the oxidation of O2− at 4.6 V versus Li+/Li on charge. These O2 molecules are reduced back to O2− on discharge, but at the lower voltage of 3.75 V, which explains the voltage hysteresis in Li-rich cathodes. 17O magic angle spinning NMR spectroscopy indicates a quantity of bulk O2 consistent with the O-redox charge capacity minus the small quantity of O2 loss from the surface. The implication is that O2, trapped in the bulk and lost from the surface, can explain O-redox.

Authors: House, RA; Rees, G; Perez-Osorio, M; Marie, J-J; Boivin, E

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: Springer Nature
• Journal: Nature Energy
• Volume: 5
• Pages: 777-785
• Publication date: 2020-09-21
• Acceptance date: 2020-08-24
• DOI: 10.1038/s41560-020-00697-2
• EISSN: 2058-7546
• ISSN: 2058-7546
• Language: English
• Keywords: FFR