Theory of coupled ion-electron transfer kinetics
Name
2007.12980.pdf
Description
Accepted version
Size
15.78 MB
Format
Adobe PDF
Checksum (MD5)
27b2a469ee8e74c15a5ae135a9ddb65f
Author(s)
Fraggedakis, Dimitrios
McEldrew, Michael
Smith, Raymond B
Krishnan, Yamini
Zhang, Yirui
Bai, Peng
Chueh, William C
Shao-Horn, Yang
Bazant, Martin Z
Date Issued
2021
Journal
Electrochimica Acta
Publisher
Elsevier BV
Version
Author's final manuscript
Abstract
© 2020 Elsevier Ltd The microscopic theory of chemical reactions is based on transition state theory, where atoms or ions transfer classically over an energy barrier, as electrons maintain their ground state. Electron transfer is fundamentally different and occurs by tunneling in response to solvent fluctuations. Here, we develop the theory of coupled ion-electron transfer, in which ions and solvent molecules fluctuate cooperatively to facilitate non-adiabatic electron transfer. We derive a general formula of the reaction rate that depends on the overpotential, solvent properties, the electronic structure of the electron donor/acceptor, and the excess chemical potential of ions in the transition state. For Faradaic reactions, the theory predicts curved Tafel plots with a concentration-dependent reaction-limited current. For moderate overpotentials, our formula reduces to the Butler–Volmer equation and explains its relevance, not only in the well-known limit of large electron-transfer (solvent reorganization) energy, but also in the opposite limit of large ion-transfer energy. The rate formula is applied to Li-ion batteries, where reduction of the electrode host material couples with ion insertion. In the case of lithium iron phosphate, the theory accurately predicts the concentration dependence of the exchange current measured by in operando X-Ray microscopy without any adjustable parameters. These results pave the way for interfacial engineering to enhance ion intercalation rates, not only for batteries, but also for ionic separations and neuromorphic computing.
MIT Department
Massachusetts Institute of Technology. Department of Chemical Engineering
Massachusetts Institute of Technology. Department of Mechanical Engineering
Massachusetts Institute of Technology. Department of Materials Science and Engineering
Massachusetts Institute of Technology. Department of Mathematics
Terms of Use
Creative Commons Attribution-NonCommercial-NoDerivs License
Persistent DSpace Link
DOI of Published Version
https://doi.org/10.1016/j.electacta.2020.137432
