The Correlation between Structure, Surface, and Performance in Fe- and Mg-Substituted LiNi0.5Mn1.5O4 Cathodes

Abstract

A need for lithium-ion cathodes that have a reduced dependence on scarce elements, such as cobalt, has been prompted by surge in eco-consciousness over the past decade. The spinel-type LiNi0.5Mn1.5O4 (LNMO) cathodes, with high operating voltages (ca. 4.7V vs Li+/Li) and energy densities (ca. 650 Wh kg-1), have received particular attention for this reason.1 Poor cycling stability, however, which arises from structural instabilities, electrolyte degradation, surface densification and loss of active material through transition metal dissolution, limits their widespread adoption.2 Elemental substitution has been employed to overcome such limitations, in which improved cycling stability has been observed. In such samples, the segregation of substituents to the cathode surface has been reported, yet the effect of surface segregation on the local atomic structure and surficial reactivity of the cathodes is under-researched.3 To further explore these areas, Fe- and Mg-substituted LNMO samples have been synthesised. Despite lower initial capacity, Mg-substituted LNMO exhibits significantly improved cycling stability over 300 cycles at 50°C. A combination of x-ray and neutron diffraction, neutron pair distribution function analysis, and x-ray absorption and photoelectron spectroscopy are used to explore the complex relationships between bulk structure, local structure, surface reactivity and performance in Fe- and Mg-substituted LNMO cathodes. References Liang, G., Peterson, V.K., See, K.W., Guo, Z., and Pang, W.K. (2020). Developing high-voltage spinel LiNi 0.5 Mn 1.5 O 4 cathodes for high-energy-density lithium-ion batteries: current achievements and future prospects . J. Mater. Chem. A.Ma, J., Hu, P., Cui, G., and Chen, L. (2016). Surface and Interface Issues in Spinel LiNi0.5Mn1.5O4: Insights into a Potential Cathode Material for High Energy Density Lithium Ion Batteries. Chem. Mater. 28, 3578–3606.Shin, D.W., Bridges, C.A., Huq, A., Paranthaman, M.P., and Manthiram, A. (2012). Role of Cation Ordering and Surface Segregation in High-Voltage Spinel LiMn LiMn 1.5Ni 0.5-xM xO 4(M = Cr, Fe, and Ga) Cathodes for Lithium-Ion Batteries. Chem. Mater. 24, 3720–3731. Figure 1