Abstract
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.
Highlights
To cite this article: Yoshiaki Murata et al 2021 J
The overvoltage is thought to be large because of the surface film produced by the decomposition of the CIPs. These results suggest that there is a trade-off between the decrease in overvoltage caused by the decrease in the desolvation energy, the formation of electrochemically unstable solvent-separated ion pairs (SSIPs)/CIP for the polarity of the solvents, and it is necessary to achieve the right balance for high stability and high electrochemical performance
We investigated the electrolyte structure using various organic solvent species and salt concentrations, and we clarified the dependency of the electrochemical performance of V2O5 nanosheet cathode materials on the electrolyte
Summary
To cite this article: Yoshiaki Murata et al 2021 J. Soc. 168 020528 View the article online for updates and enhancements. Manuscript submitted August 13, 2020; revised manuscript received January 7, 2021. This was paper 2408 presented at the Atlanta, Georgia, Meeting of the Society, October 13–17, 2019
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