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

DOI: 10.1038/s41560-020-00697-2

Authors: Robert A. House (University of Oxford; The Henry Royce Institute; The Faraday Institution) , Gregory J. Rees (University of Oxford; The Henry Royce Institute; The Faraday Institution) , Miguel A. Pérez-Osorio (University of Oxford; The Henry Royce Institute; The Faraday Institution) , John-Joseph Marie (University of Oxford; The Henry Royce Institute; The Faraday Institution) , Edouard Boivin (University of Oxford; The Henry Royce Institute) , Alex W. Robertson (University of Oxford; The Henry Royce Institute) , Abhishek Nag (Diamond Light Source) , Mirian Garcia-Fernandez (Diamond Light Source) , Ke-Jin Zhou (Diamond Light Source; Swiss Light Source) , Peter G. Bruce (University of Oxford; The Henry Royce Institute; The Faraday Institution)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Nature Energy , VOL 137

State: Published (Approved)
Published: September 2020
Diamond Proposal Number(s): 23889

Abstract: 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.

Journal Keywords: Batteries; Electrochemistry; Materials for energy and catalysis

Diamond Keywords: Batteries; Lithium-ion

Subject Areas: Materials, Chemistry, Energy


Instruments: I21-Resonant Inelastic X-ray Scattering (RIXS)

Added On: 25/09/2020 08:56

Discipline Tags:

Energy Storage Energy Physical Chemistry Energy Materials Chemistry Materials Science

Technical Tags:

Scattering Spectroscopy Resonant Inelastic X-ray Scattering (RIXS) X-ray Absorption Spectroscopy (XAS)