Vertical Distribution of Overpotentials and Irreversible Charge Losses in Lithium Ion Battery Electrodes

• Published in: ChemSusChem Vol. 7; no. 8; pp. 2159 - 2166
• Main Authors: Klink, Stefan, Schuhmann, Wolfgang, La Mantia, Fabio
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 01.08.2014; WILEY‐VCH Verlag; Wiley Subscription Services, Inc
• Subjects: Batteries; Electric Power Supplies; Electrochemistry; Electrodes; Electrolytes - chemistry; Graphite - chemistry; irreversible charge losses; Lithium; Lithium - chemistry; lithium-ion batteries; Models, Chemical; multi-layered working electrode; Porosity; porous electrodes; multi-layered working electrode; irreversible charge losses; lithium-ion batteries; electrochemistry; porous electrodes
• ISSN: 1864-5631; 1864-564X
• DOI: 10.1002/cssc.201400056

Porous lithium ion battery electrodes are characterized using a vertical distribution of cross‐currents. In an appropriate simplification, this distribution can be described by a transmission line model (TLM) consisting of infinitely thin electrode layers. To investigate the vertical distribution of currents, overpotentials, and irreversible charge losses in a porous graphite electrode in situ, a multi‐layered working electrode (MWE) was developed as the experimental analogue of a TLM. In this MWE, each layer is in ionic contact but electrically insulated from the other layers by a porous separator. It was found that the negative graphite electrodes get lithiated and delithiated stage‐by‐stage and layer‐by‐layer. Several mass‐transport‐ as well as non‐mass‐transport‐limited processes could be identified. Local current densities can reach double the average, especially on the outermost layer at the beginning of each intercalation stage. Furthermore, graphite particles close to the counter electrode act as “electrochemical sieve” reducing the impurities present in the electrolyte such as water. Electrochemical sieving: Porous electrodes are characterized by a vertical distribution of cross currents. In an appropriate simplification, the cross‐current distribution can be described by a transmission line model consisting of thin electrode layers. Using a multi‐layered working electrode as experimental analogue of the transmission line model, it is shown that electrolyte additives and contaminants are unevenly reduced in graphite lithium ion battery electrodes during the first charge.