Tailoring room-temperature miscibility gap in ordered spinel LiNi0.5Mn1.5O4 cathodes by multi-element doping

Abstract

In the pursuit of improved lithium-ion battery performance, the ordered spinel LiNi_0.5Mn_1.5O₄ (LNMO) cathode material stands out as promising candidate because of its 5 V level operating voltage. However, problems of capacity degradation due to both leaching of Mn²⁺ via a side reaction with electrolyte and a large strain formed inside the particle by the two-phase reaction model hinder its practical application. This study investigates the effect of multiple element doping (Si, Ti, Ge) on charge/discharge reaction mechanisms of LNMO cathodes to mitigate the capacity degradation, caused by the large strain. Structural and electrochemical changes induced by doping were analyzed coupled with operando XRD, ex-situ XAFS, and theoretical calculations with a universal neural network potential. The results demonstrate that multi-element doping enhances structural stability, tailored charge/discharge reaction mechanisms, and improves cyclability. The doped LNMO cathode exhibited an altered charge-discharge voltage profile showing the deviation of the capacity-voltage curve from the constant potential, suggesting a shift in the reaction mechanism toward a solid solution model. The corresponding solid solution ranges outside the miscibility gap (Li_1.0NMO/Li_0.5NMO and Li_0.5NMO/ Li_0.0NMO) due to multiple-element doping were found to significantly reduce strain formation, leading to enhanced performance. Overall, this study provides a comprehensive understanding of the effects of multi-element doping on LNMO cathodes and highlights the potential of this strategy to address the limitations of current lithium-ion battery technology.