Detection of trapped molecular O2 in a charged Li-rich cathode by Neutron PDF
Understanding the fundamental charge storage mechanisms of high energy density cathode materials is critical to realising the next generation of Li-ion batteries. Oxygen redox is one possible route to achieve this goal, but there has been intense debate of the nature of the O-redox process and how best to exploit it.
In their research article published in Energy & Environmental Science, Dr Robert House and Professor Peter Bruce from Oxford Materials and the Faraday Institution's CATMAT project employed neutron total scattering to obtain the first direct structural evidence of trapped oxygen molecules in charged Li-rich battery cathodes. The formation and reduction of trapped O2 during charge and discharge respectively offers a plausible mechanism for O-redox. Neutron total scattering offers the unique ability to probe local structure in the bulk of solid materials. The data revealed the presence of atoms separated by a distance of 1.2A in the battery cathode, corresponding to the O-O bond length in molecular O2.
They were further able to show how careful morphological control of the Li-rich cathode particles can suppress O2 evolution and favour the trapping of more molecular O2 in the bulk. This leads to substantial improvement in the first cycle coulombic efficiency of the oxygen redox reaction, leading to a cathode material of greater energy density. This understanding will help inform efforts to tailor the morphology of Li-rich cathodes to improve their performance.
This work was conducted in close collaboration with scientists at the POLARIS instrument (ISIS Neutron Source), Beamline 121 (Diamond Light Source) and the David Cockayne Centre for Electron Microscopy (Oxford Materials).
