School of Chemistry Colloquium: Professor Louis Piper (University of Warwick) The big "O" in battery research

The 3d transition metal layered oxide cathodes derived from LiCoO2 are critical components of our lithium-ion battery technology, due to their high energy density and rate performance. In simple terms the Co and Ni ions in the cathode are expected to oxidize to formal 4+ states when are the lithium ions are extracted. However, in real Li-ion batteries, the layered oxides are never fully delithiated during cycling because of degradation issues at high states of charge, i.e., above 2/3 of lithium extraction. The oxygen anions are considered to be largely inert bystanders in the redox process despite oxygen loss being a major degradation and safety concern. Are oxygen ions participating in the redox and is the ionic approximation of inert O2- ions “Goodenough” (pun intended)?
Oxygen redox has often been reported in terms of O-O dimer formation and is considered distinct from conventional redox mechanisms in stoichiometric layered cathodes. By considering Ni-rich layered oxides as negative charge transfer insulators, I will demonstrate studies that confirm how oxygen participation in charge compensation naturally arises from ligand holes (i.e., L, charge transfer from O2p orbitals) without necessarily requiring O2 formation. As a result, Ni2+/4+ redox is better reflected in terms of electron transfer involving changes in the electron density on the oxygen ions i.e. ligand holes (L). The implications are discussed in terms of gas evolution and design principles for next generation cathodes such as protective coatings.

This event is open to final year undergraduate students, MSc students, PhD students, post-doctoral research associates and academic staff.