Combining electrochemistry, XRD & Raman spectroscopy, and density functional theory to investigate the fundamentals of LiCO formation in supercapacitors

• Published in: Journal of materials chemistry. A, Materials for energy and sustainability Vol. 11; no. 38; pp. 2636 - 265
• Main Authors: Freitas, Bruno, Nunes, Willian G, Real, Carla G, Rodella, Cristiane B, Doubek, Gustavo, da Silva, Leonardo, Thaines, Ericson H. N. S, Pocrifka, Leandro A, Freitas, Renato G, Zanin, Hudson
• Format: Journal Article
• Published: 04.10.2023
• DOI: 10.1039/d3ta02182c
• ISSN: 2050-7488

Higher voltage aqueous electrolytes in supercapacitors are a promising technology in energy storage applications due to their high power, low cost, and environmental friendliness. However, applying voltages under abusive conditions would cause damage or failure to the cell. Here, we report the transient modification of the electrode & electrolyte interface tracked by operando synchrotron X-ray diffraction and Raman spectroscopy analysis combined with in situ electrochemistry and theoretical calculations to explore the formation of lithium carbonate species and reversible degradation in supercapacitors. Symmetrical electrochemical supercapacitors were prepared with nickel oxide (NiO) decorated multiwalled carbon nanotube (MWCNT) electrodes and filled with 1.0 mol L −1 Li 2 SO 4 aqueous electrolyte. Operando XRD analysis of NiO@MWCNT shows crystalline Li 2 CO 3 formation when applying higher operating cell voltages, close to 2.0 V, in anodic polarization and decomposition in the cathodic polarization, evidencing the reversibility of the system. Studies by operando Raman spectroscopy showed that the carbon electrodes oxidise with structural changes on the carbon electrode surface. A theoretical analysis is presented to relate the effect of Li 2 CO 3 formation on the electronic properties. Li 2 CO 3 formation deformed the electron localization function of nanotubes, suggesting that Li-ion diffusion can be restricted, influencing Li 2 CO 3 formation and reversible decomposition. A plausible reason for Li 2 CO 3 formation is CO 2 evolution due to the degradation of the MWCNT electrode and Li + ions from the electrolyte, catalysed by NiO nanoparticles. Interestingly, Li 2 CO 3 formation is reversible on the full cycle cell scan in the presence of NiO, being able to explore different applications in energy storage. This study combines operando XRD & Raman spectroscopy and DFT simulation to reveal how Li 2 CO 3 formation and reversibility may contribute to energy storage in supercapacitors.