The role of Ni and Co in suppressing O‐loss in Li‐rich layered cathodes

DOI: 10.1002/adfm.202003660

Authors: Edouard Boivin (University of Oxford) , Niccolo Guerrini (University of Oxford) , Robert A. House (University of Oxford) , Juan G. Lozano (University of Oxford) , Liyu Jin (University of Oxford) , Gregory J. Rees (University of Oxford) , James W. Somerville (University of Oxford) , Christian Kuss (University of Oxford) , Matthew R. Roberts (University of Oxford) , Peter G. Bruce (University of Oxford)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Advanced Functional Materials

State: Published (Approved)
Published: August 2020

Abstract: Lithium‐rich transition metal cathodes can deliver higher capacities than stoichiometric materials by exploiting redox reactions on oxygen. However, oxidation of O2− on charging often results in loss of oxygen from the lattice. In the case of Li2MnO3 all the capacity arises from oxygen loss, whereas doping with Ni and/or Co leads to the archetypal O‐redox cathodes Li[Li0.2Ni0.2Mn0.6]O2 and Li[Li0.2Ni0.13Co0.13Mn0.54]O2, which exhibit much reduced oxygen loss. Understanding the factors that determine the degree of reversible O‐redox versus irreversible O‐loss is important if Li‐rich cathodes are to be exploited in next generation lithium‐ion batteries. Here it is shown that the almost complete eradication of O‐loss with Ni substitution is due to the presence of a less Li‐rich, more Ni‐rich (nearer stoichiometric) rocksalt shell at the surface of the particles compared with the bulk, which acts as a self‐protecting layer against O‐loss. In the case of Ni and Co co‐substitution, a thinner rocksalt shell forms, and the O‐loss is more abundant. In contrast, Co doping does not result in a surface shell yet it still suppresses O‐loss, although less so than Ni and Ni/Co doping, indicating that doping without shell formation is effective and that two mechanisms exist for O‐loss suppression.

Journal Keywords: cathodes; Li‐ion batteries; Li‐rich layered oxides; oxygen loss; oxygen redox

Subject Areas: Materials, Chemistry, Energy


Instruments: B18-Core EXAFS

Documents:
adfm.202003660.pdf