(294f) Modeling Mechanisms of Nickel Oxide Lithiation Using First Principles Calculations and Classical Nucleation Theory

Metal oxide conversion reactions present an opportunity for ultrahigh high capacity lithium ion battery electrodes, wherein the direct reaction of lithium ions with lattice oxygen anions leads to a discharge product consisting of metal nanoparticles embedded in a matrix of amorphous lithia (a-Li₂O). Despite the promise of such chemistries, there exist many challenges toward their practical implementation. Of primary concern for these materials is the presence of large overpotentials, which lead to significant voltage hysteresis between charge and discharge cycles.¹ For example, nickel oxide (NiO) lihiates at 0.6 V, whereas the bulk reduction potential is at 1.86 V.² To address these concerns, nanoscale interfacial engineering has been shown to enhance the reversibility of conversion reactions and reduce overpotentials.^3,4 In this work, we use density functional theory (DFT) and classical molecular dynamics (MD) calculations to understand interfacial reactions for the NiO conversion reaction. DFT-calculated interfacial energies for Ni|a-Li₂O, Ni|NiO, and NiO|a-Li₂O interfaces are performed, and integrated into a classical nucleation theory (CNT) model. This DFT-MD-CNT computational approach is used to calculate potential-dependent nucleation barriers and is compared to structural details obtained from in operando synchrotron X-ray scattering experiments on multilayer Ni|NiO thin film electrodes. In agreement with experimentally observed high voltage changes in electron density at the multilayer interface, we determine that a lithium-rich region at the Ni|Li₂O interface significantly lowers the predicted nucleation barrier. This result is consistent with mechanisms for capacitive interfacial charge storage in other conversion reaction materials.⁵

This research was supported as part of the Center for Electrochemical Energy Science, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.

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