Electrolyte Dependency on Ca2+ Insertion and Extraction Properties of V2O5

The influence of the electrolyte structure on the Ca2+ ion insertion and extraction properties of V2O5 was studied by changing the electrolyte concentration or solvent. The electrolyte structure was analyzed by Raman spectroscopy. The most significant changes were found in the molar ratio of the contact ion pair (CIP) in the total ionic species. Among the various electrolytes, 0.3 M Ca(TFSI)(2) dissolved in ethylene carbonate and dimethyl carbonate (0.3 M EC:DMC) and 0.5 M Ca(TFSI)(2) dissolved in triglyme (0.5 M G3) have relatively small molar ratios of CIPs. The electrochemical performance was strongly related to the molar ratio of the CIPs. A high coulombic efficiency and high capacity were observed when using 0.3 M EC-DMC. Moreover, 0.5 M G3 showed the highest capacity despite its low coulombic efficiency. This could be related to the formation of solvent-separated ion pairs (SSIPs) due to the low polarity of G3 and its solvation form that encapsulates Ca2+. SSIPs had a reductively unstable character as that of the CIPs. Surface analysis revealed that the thinner the surface film produced, the lower the CIP content. This was deemed responsible for the rate performance enhancements, given the potential electrochemical instability of the Ca-containing CIPs.

Automated summary

The study investigated the influence of electrolyte structure on the Ca2+ ion insertion and extraction properties of V2O5 by changing the concentration or solvent. It was found that the molar ratio of contact ion pairs (CIP) in the total ionic species significantly affected the electrochemical performance. Different electrolytes showed varying capacity and coulombic efficiency, with solvent-separated ion pairs (SSIPs) potentially contributing to performance differences.