Exploring carbon electrode parameters in Li-O cells: LiO and LiCO formation

• Published in: Journal of materials chemistry. A, Materials for energy and sustainability Vol. 12; no. 12; pp. 7215 - 7226
• Main Authors: Sousa, Bianca P, Anchieta, Chayene G, Nepel, Thayane M. C, Neale, Alex R, Hardwick, Laurence J, Filho, Rubens M, Doubek, Gustavo
• Format: Journal Article
• Published: 19.03.2024
• ISSN: 2050-7488; 2050-7496
• DOI: 10.1039/d3ta07701b

Ensuring the stability of the electrode and electrolyte in Li-O 2 batteries and achieving a comprehensive understanding of parasitic side reaction management during cycling are key issues for the progress of this promising energy storage technology. Conditions that favour formation of either Li 2 O 2 or Li 2 CO 3 in Li-O 2 cells on carbon-based electrodes were investigated. Operando Raman microscopy measurements and ex situ Raman and X-ray photoelectron spectroscopy (XPS) analyses were performed for Li-O 2 systems using Li[ClO 4 ]/DMSO as the electrolyte and carbon paper (CP) and carbon paper with carbon nanotubes (CPCNT) as electrodes. Using CP electrodes (either treated or untreated with O 2 plasma), the major discharge product formed was Li 2 O 2 . In contrast, for CPCNT electrodes, the formation of Li 2 CO 3 as the main discharge product was observed at lower capacities, then significant formation of Li 2 O 2 proceeded at higher discharge capacities. XPS highlighted that the surface chemistry of the CPCNT electrode comprised fluorine and a variety of iron species, which could be linked to the promotion of Li 2 CO 3 formation. Furthermore, it was observed that when Li 2 CO 3 is the main discharge product, the active sites of functional groups on carbon surfaces that favour carbonate formation become coated/passivated. Consequently, the dominant reaction pathway then alters, leading to the growth of Li 2 O 2 over the surface. These outcomes emphasized the important role in cycling stability of the active sites on carbon electrodes, arising from the synthesis process or possible contaminants. Different discharge products were revealed in Li-O 2 batteries with different carbon cathodes by operando Raman and ex situ Raman and XPS measurements. In a carbon paper electrode Li 2 O 2 is formed, while for electrodes with CNT, Li 2 CO 3 and Li 2 O 2 were noticed in different discharge stages.