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

Abstract

An <i>operando</i> dual-edge X-ray absorption spectroscopy on both transition-metal ordered and disordered LiNi_0.5Mn_1.5O₄ 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 Ni^2+/4+ redox couple involving a transient Ni³⁺ phase. Interestingly, a reversible minority contribution of Mn^3+/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.