Alkali-Metal Insertion Processes on Nanospheric Hard Carbon Electrodes: An Electrochemical Impedance Spectroscopy Study

Abstract

© The Author(s) 2017. Published by ECS. All rights reserved. In this study, we report the results of electrochemical impedance spectroscopy data modelling of various battery half-cells with different alkali metal (Li, Na, K) salts. Test results of electrochemical half-cells were evaluated for the D-glucose derived hard carbon negative electrode in 1.0 M LiPF6+ EC:DMC (1:1 volume ratio), 1.0 M NaPF6+ EC:DMC (1:1), 1.0 M NaClO4+ PC, 0.8 M KPF6+ EC:DEC (1:1) and 0.8 M KPF6+ EC:DMC (1:1) solutions at 0.5 mV s−1potential scan rate measured within the potential region from 0.05 V to 1.2 V (vs Me/Me+) (where Me is Li, Na or K). Modelling of electrochemical impedance spectroscopy data was employed to characterize alkali metal insertion processes in/on D-glucose derived hard carbon anode. Detailed analysis of impedance data shows that Newman equivalent circuit modified with a constant phase element can be applied for calculation of impedance spectra and fitting of calculated data to experimental ones, using non-linear least square root fitting method. Equivalent circuit fit parameters depend strongly on electrolyte composition. Very slow processes have been observed for KPF6+ EC:DEC based half-cell. Comparatively quick metal-cation reduction and accumulation processes have been observed in NaClO4+ PC and LiPF6+EC:DMC based half-cell anodes.