Influence of Transition-Metal Order on the Reaction Mechanism of LNMO Cathode Spinel: An Operando X-ray Absorption Spectroscopy Study

An operando dual-edge X-ray absorption spectroscopy on both transition-metal ordered and disordered Li-Ni0.5Mn1.5O4 during electrochemical delithiation and lithiation was carried out. The large data set was analyzed via a chemometric approach to gain reliable insights into the redox activity and the local structural changes of Ni and Mn throughout the electrochemical charge and discharge reaction. Our findings confirm that redox activity relies predominantly on the Ni2+/4+ redox couple involving a transient Ni3+ phase. Interestingly, a reversible minority contribution of Mn3+/4+ is also evinced in both LNMO materials. While the reaction steps and involved reactants of both ordered and disordered LNMO materials generally coincide, we highlight differences in terms of reaction dynamics as well as in local structural evolution induced by the TM ordering.

Automated summary

This study performed operando dual-edge X-ray absorption spectroscopy on both transition-metal ordered and disordered Li-Ni0.5Mn1.5O4 materials during the electrochemical delithiation and lithiation process. The analysis of a large dataset using a chemometric approach provided reliable insights into the redox activity and local structural changes of Ni and Mn. The results confirm the dominant redox activity of the Ni2+/4+ redox couple involving a transient Ni3+ phase, and also highlight a reversible minority contribution of Mn3+/4+ in both LNMO materials. While the reaction steps and involved reactants are generally similar in ordered and disordered LNMO materials, differences in reaction dynamics and local structural evolution induced by TM ordering are emphasized.