First Principles Calculations of Interfacial Models for Nucleation Processes during NiO Conversion Reactions

Abstract

Oxide conversion reactions may yield Li-ion battery electrodes with exceptionally high capacities in comparison to intercalation materials, with Li2O-encompassed transition metal nanoparticles as the ideal discharge product. Nanoscale confinement has been demonstrated to facilitate the reversibility of these conversion reactions1–3. The NiO conversion reaction, in particular, has a high theoretical capacity (718 mAh g-1), but there is significant hysteresis between the experimental and theoretical voltage (0.6 V and 1.9 V, respectively), and the molecular origins of this hysteresis are poorly understood. In this work, we will present an integrated computational modeling approach, using classical molecular dynamics and first principles density functional theory calculations, with classical nucleation theory, to directly probe the role of interfaces during NiO conversion. These efforts are informed, in part, by recent work suggesting a strong role of interfaces during conversion, as lithiated domains propagate from the surface to the bulk of NiO nanomaterials4. Different nucleation schemes are evaluated, considering potential-dependent bulk and interfacial free energies to determine critical nucleation radii and energy barriers, as well as possible mechanisms for exceeding theoretical capacity limits. Theoretical predictions are directly compared to experimentally observed Ni/NiO multilayer electrode morphologies determined from in-situ X-ray reflectivity measurements. 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.