Interactions between electrolyte constituents and active materials strongly influence the capacity, energy density, and cycling stability of energy storage devices. In this study, the role of electrolyte dielectric on the...
Lithium‐ion capacitors (LICs) represent promising high power energy storage devices, most commonly composed of a Li‐ion intercalation anode (e.g., graphite or hard carbon), a supercapacitor activated carbon (AC) cathode, and an electrolyte with 1 M LiPF6 in carbonate solvents. Here, we report on the feasibility of replacing LiPF6 with the novel salt LiFSI for use with AC electrodes. Based on voltage hold measurements in a half‐cell setup, good long‐term stability is achieved with an upper cut‐off voltage of 3.95 V vs. Li/Li+, potentially enabling cell voltages of ~3.8 V when combined with graphite anodes (operating at ~0.1 V vs. Li/Li+) in LIC full cells. The systematic comparison of cyclic voltammetry, leakage current analysis, and capacity retention upon voltage hold highlights the importance of the latter method to provide a realistic assessment of the electrochemical stability window of LiFSI on AC. The morphological and surface‐chemical post‐mortem analysis of AC electrodes used with LiFSI revealed that the oxidation of the FSI anion, as evidenced by the presence of new S 2p and N 1s features in the XPS spectra, and an increasing amount of oxygenated species on the AC were the main processes causing capacity fade at positive polarization.
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