Charge transfer kinetics at the solid–solid interface in porous electrodes

• Published in: Nature communications 2014-04, Vol.5 (1), p.3585-3585, Article 3585
• Main Authors: Bai, Peng, Bazant, Martin Z.
• Format: Article
• Language: English
• Subjects: 639/301/299/161; Carbon; Electrodes; Electrolytes; Electrons; Energy; Humanities and Social Sciences; Interfaces; Lithium; multidisciplinary; Science; Science (multidisciplinary)
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/ncomms4585

Interfacial charge transfer is widely assumed to obey the Butler–Volmer kinetics. For certain liquid–solid interfaces, the Marcus–Hush–Chidsey theory is more accurate and predictive, but it has not been applied to porous electrodes. Here we report a simple method to extract the charge transfer rates in carbon-coated LiFePO 4 porous electrodes from chronoamperometry experiments, obtaining curved Tafel plots that contradict the Butler–Volmer equation but fit the Marcus–Hush–Chidsey prediction over a range of temperatures. The fitted reorganization energy matches the Born solvation energy for electron transfer from carbon to the iron redox site. The kinetics are thus limited by electron transfer at the solid–solid (carbon-Li x FePO 4 ) interface rather than by ion transfer at the liquid–solid interface, as previously assumed. The proposed experimental method generalizes Chidsey’s method for phase-transforming particles and porous electrodes, and the results show the need to incorporate Marcus kinetics in modelling batteries and other electrochemical systems. Electrochemical kinetics are usually described by the Butler–Volmer equation. Bai and Bazant propose a method to extract reaction rates for porous electrodes from experiments and show the necessity of using Marcus charge transfer theory in place of the conventional kinetics.