Solvation-Reduction Coupling in Ca2+ Electroactivity in Glyme-Based Electrolytes: A First Principles Study

The electrochemical activity of solvated Ca2+ in glyme-based electrolytes is investigated using grand canonical density functional theory approach and Fukui functions. The obtained results reveal that the length of glyme molecules has little effect on the reduction potentials, but has significant impacts on the effective electron transfer process. In short chain glymes, the transferred electron is located on a Ca2+ center and the organic part of the solvation sphere, leading to a direct Ca2+ reduction and a partial degradation of the glyme molecules. As the glyme's length increases, the reduction process turns into the formation of solvated electrons rather than Ca2+ reduction, unless a partial desolvation occurs. Consequently, an effective Ca2+ reduction in long chain glyme-based electrolytes is controlled by a (partial) desolvation of the solvation sphere. These results can be used as guiding information to design new electrolytes having the Ca2+ reduction potential in an accessible voltage range together with an effective Ca2+ reduction process. The methodology developed in this study can be universally applied to investigate the thermodynamic and kinetic properties of other battery systems using metal anodes, which might lead to a paradigm shift in the design of prospective electrolytes for future battery technologies.

Automated summary

This study investigates the electrochemical activity of solvated Ca2+ in glyme-based electrolytes using grand canonical density functional theory and Fukui functions. The results show that the length of glyme molecules has little influence on the reduction potentials, but significantly affects the effective electron transfer process. In short chain glymes, the transferred electron is located on a Ca2+ center and the organic part of the solvation sphere, which leads to direct Ca2+ reduction and partial degradation of glyme molecules. As the glyme's length increases, the reduction process shifts to the formation of solvated electrons instead of Ca2+ reduction, unless partial desolvation occurs. Therefore, effective Ca2+ reduction in long chain glyme-based electrolytes is controlled by (partial) desolvation of the solvation sphere. These findings can guide the design of new electrolytes with Ca2+ reduction potential in an accessible voltage range and an effective reduction process. The methodology developed in this study can be universally applied to investigate the properties of other metal anode battery systems, potentially revolutionizing the design of prospective electrolytes for future battery technologies.