Substituting Critical Materials in Positive Electrodes for Li-Ion Batteries— Implications for the Electrode-Electrolyte Reactivity

Nickel-rich layered oxides are promising positive electrode materials for Li-ion batteries, due to their high specific energy on the first cycles and the substitution of the traditionally used Co for the less critical element Ni. Despite these promises, these materials are characterized by striking performance degradation, accompanied by the building of electrode-electrolyte interfacial impendence. Understanding the (electro)chemical reactions at the interface between the positive electrode and the organic electrolyte is crucial for the rational design of sustainable Li-ion batteries with improved safety, capacity retention and cycle life. Density Functional Theory (DFT) calculations demonstrated that solvent C-H dissociation, accompanied by an interfacial charge transfer, occurs for organic carbonates at the surface of Li_xMO₂. The driving force for the interfacial reactivity depends on the oxide composition and increases on oxide surfaces with transition metal ions from left to right in the periodic table and by increasing transition metal oxidation state upon delithiation, with the position of oxide O 2<i>p</i> band center with respect to the Fermi level serving as a reactivity descriptor [1]. These findings were used to identify a design principle for the screening of coating materials which can prevent the dissociation of organic carbonates [2]. Here we use DFT calculations to analyze the stability trends for Li- and Na-batteries positive electrode materials as a function of the transition metal and state of charge, which are used to rationalize the observed degradation mechanisms. These results are leveraged to identify stability descriptors for positive electrode materials that can be used for the design of novel positive electrode materials [3].<br/><br/>[1] L. Giordano, P. Karayaylali, Y. Yu, Y. Katayama, F. Maglia, S. Lux, Y. Shao-Horn, <i>J. Phys. Chem. Lett</i>, 8, 3881 (2017).<br/>[2] L. Giordano, T. M. Østergaard, S. Muy, Y. Yu, N. Charles, S. Kim, Y. Zhang, F. Maglia, R. Jung, I. Lund, J. Rossmeisl, Y. Shao-Horn, <i>Chem. Mater.</i> 31, 5464 (2019).<br/>[3] V. Sanella, L. Giordano, in preparation.