Employing anionic redox chemistry to tune the electrochemical performance of Li-ion batteries

Andreas Paulusa, Marlies K. Van Baela
Hasselt University, Institute for Materials Research (imo-imomec) and imec, division imomec, DESINe team, Agoralaan Gebouw D, 3590 Diepenbeek, Belgium
EnergyVille, Thor Park 8320, 3600 Genk, Belgium

Mylène Hendrickx, Joke Hadermann, An Hardy
University of Antwerp, Electron Microscopy for Materials Science (EMAT), Groenenborgerlaan 171, 2020 Antwerpen, Belgium

Peter Adriaensens
Hasselt University, Institute for Materials Research (imo-imomec), NMR group, Agoralaan Gebouw D, 3590 Diepenbeek, Belgium

Corresponding author: andreas.paulus@uhasselt.be

Charge compensation for sulfide-type cathode materials for Li-ion batteries by redox chemistry of the sulfide sublattice is already know for decades. More recently, the remarkably high reversible capacity in specific Li-rich layered metal oxide cathode materials for Li-ion batteries has been associated with the contribution of anionic redox chemistry of the oxygen sublattice (i.e. oxidation of O2- during lithium-ion extraction from the cathode material during charging of a battery), on top of cationic redox chemistry of redox-active transition metal ions.

In this lecture, the concepts of anionic redox chemistry in Li-rich layered oxide cathode materials for Li-ion batteries will be introduced. By the Mott-Hubbard vs. charge-transfer approach, the reversibility of the anionic redox of the oxygen sublattice will be correlated to the structural and chemical nature of Li-rich layered oxide cathode materials. It will be deduced that for 3d transition metal-containing Li-rich layered oxide cathode materials the anionic redox chemistry is to a lower extent reversible compared to their 4d and 5d transition metal-containing counterparts. Irreversible anionic redox chemistry implies the release of O2, accompanied with a degradation of the initial layered structure to a spinel-type and eventually a rock salt-type structure, penalizing the energy density (i.e. voltage fade). As commercialization of the latter (e.g. Li2RuO3 or Li2IrO3) is not feasible due to the scarcity and high price of the respective 4d and 5d transition metals, improving the reversibility of the anionic redox chemistry, coupled with cationic redox, of 3d transition metal-containing Li-rich oxides is of great interest.

A potential strategy to inhibit voltage fade is to stabilize the layered structure by partial substitution of redox-active transition metal cations by redox inactive, isovalent cations, showing a stronger metal-oxygen bonding. The second part of this lecture will focus on the implementation of Ti4+ substitution in Li2MnO3 to understand its influence on the anionic redox and the electrochemical performance when applied as a cathode material for Li-ion batteries.

The authors acknowledge Research Foundation Flanders (FWO) project number G040116N for funding. The authors also acknowledge support by Hasselt University and the Research Foundation Flanders for the Hercules project AUHL/15/2- GOH3816N.

Andreas Paulus obtained a PhD in chemistry from Hasselt University (Belgium) in 2021 on the effect of cationic substitutions on anionic redox chemistry in rock salt-type layered Li-rich metal oxide cathode materials for Li-ion batteries. During his PhD, there has been a strong emphasis on solution-based synthesis methods to obtain the desired cation substituted cathode materials. During his PhD, he fulfilled a research stay at the Skolkovo Institute of Science and Technology (Russia), to strengthen his knowledge on co-precipitation synthesis and X-ray diffraction. Currently, he is performing research on novel Co-free metal oxide cathode materials for Li-ion batteries as a R&D Engineer employed by Imec (Interuniversity Microelectronics Centre) on the Horizon 2020 co-funded project ‘Cobra’.