Carbon as Quasi-Reference Electrode in Unconventional Lithium-Salt Containing Electrolytes for Hybrid Battery/Supercapacitor Devices

Abstract

Metallic lithium is the most widespread reference electrode in lithium ion battery research, but its high reactivity limits the usage primarily to conventional carbonate based electrolytes. Novel high power concepts, like hybrid supercapacitors, require lithium containing electrolytes with high ionic conductivity (e.g., acetonitrile), which are not always stable versus lithium. In the current work we face this issue by refining activated carbon as a quasi-reference electrode originally employed for conventional supercapacitors. Different commercially available carbon powders were examined as reference electrode materials and calibrated in lithium-salt containing acetonitrile versus Li + intercalation/de-intercalation reaction of nanoparticulate Li 4 Ti 5 O 12 . The stability of the activated carbon reference electrode is highly affected by the salt employed and decreases in the following order: LiTFSI > LiClO 4 > LiPF 6 > LiBF 4 . Only a negligible impact of electrolyte solvent, pore size distribution and reference electrode binder was observed. Furthermore, activated carbon was functionalized (HNO 3 treated) and de-functionalized (thermal annealing in vacuum or hydrogen) to investigate the impact of carbon functionalization on the reference electrode stability. Nitrogen and oxygen containing surface groups have been found to drastically improve long-term stability of activated carbon quasi-reference electrodes. Even after 15 days exposed to the electrolyte, the potential of HNO 3 treated activated carbon is marginally altered by 10 mV.

Valence‐Tuned Lithium Titanate Nanopowder for High‐Rate Electrochemical Energy Storage

“…The counter electrode was prepared by mixing YP‐50F with isopropanol in a DAC400 FVZ speed mixer at 2500 rpm . This treatment was followed by 7 min sonication and subsequent 4 min mixing at 2500 rpm.…”

“…[59]. The functionalization of AC introduces nitrogen and oxygen containing functional groups on the carbon surface, which drastically stabilize the QRE stability . The functionalized AC and PTFE powders (PTFE 6 CN X, DuPont) were dried at 120 °C under vacuum for 12 h before being introduced to the glovebox.…”

High-throughput battery materials testing based on test cell arrays and dispense/jet printed electrodes

“…Porous carbon electrodes can be fabricated by electrophoretic deposition, dispensing or spray deposition. Those carbonaceous materials had a low potential drift over days as well as a high tolerance for impurities (Maminska et al 2006;Saheb et al 2006;Weingarth et al 2012a, b;Widmaier et al 2016). We here investigated the use of LTO MPREs for lithium-ion cells; since LTO is one of the anode materials, it requires no additional fabrication effort.…”

Gyroidal Porous Carbon Activated with NH3 or CO2 as Lithium−Sulfur Battery Cathodes

“…Nitrogen can also enhance the activity towards sulfur reduction and, thereby, provides a higher initial capacity ,,. The many methods to produce nitrogen‐doped porous carbon mainly follow two approaches: either direct pyrolysis of nitrogen‐containing precursors (e. g., melamine resin, polypyrrole, or biomass) or post‐synthesis treatment of carbon with nitrogen‐containing compounds (e. g., NH 3 , HCN, or HNO 3 ,). One disadvantage of the direct use of nitrogen‐containing precursors is that the functional groups may be released at high pyrolysis temperatures .…”

“…In contrast, post‐synthesis treatments are an elegant way to modify a given material without changing the initial reaction parameters. However, this approach might form additional functional surface groups instead of actual nitrogen doping ,,. Wang et al.…”