Effect of Alkaline-Basic Electrolytes on the Capacitance Performance of Biomass-Derived Carbonaceous Materials

Abstract

<jats:p>The present work explores in detail the effect of alkaline-basic electrolytes on the capacitance performance of biomass-derived carbonaceous materials used as electrodes in symmetric supercapacitors. The proof-of-concept is demonstrated by two commercial carbon products (YP-50F and YP-80F, Kuraray Europe GmbH, Vantaa, Finland), obtained from coconuts. The capacitance performance of YP-50F and YP-80F was evaluated in three types of basic electrolytes: 6 M LiOH, 6 M NaOH and 6 M KOH. It was found that the capacitance performance of YP-50F improved in the following order: NaOH &lt; LiOH &lt; KOH; Meanwhile, for YP-80F, the order changes to LiOH &lt; NaOH &lt; KOH. After 1000 cycles, the cycling stability of both YP-50F and YP-80F increased in the order NaOH &lt; LiOH &lt; KOH. This order of performance improvement is determined by both the electrolyte conductivity and the interaction between the functional groups of carbonaceous materials and alkaline electrolytes. The reactivity of the functional groups was assessed by postmortem SEM/EDS and X-ray photoelectron spectroscopy (XPS) analyses of the electrodes after prolonged cycling.</jats:p>

Biomass-Derived Carbonaceous Materials to Achieve High-Energy-Density Supercapacitors

“…In the narrow voltage window (i.e., between 0.6 and 2.4 V for lithium electrolyte and between 0.1 and 2.6 V for sodium electrolyte), the rate capability of YP-50F is improved significantly. The obtained capacitance values for YP-50F in lithium and sodium organic electrolytes are lower than those in aqueous electrolytes (i.e., 6 M LiOH and 6 M NaOH) (Karamanova et al, 2020): at a current load of 60 mA/g the capacitance is about 80 F/g in LiBF 4 and NaPF 6 vs. 113 F/g and 108 F/g in LiOH and NaOH, respectively. It should be taken into account that these capacitance values are reached in different voltage window: 1.8 V for LiPF 6 and LiBF 4 , 2.5 V for NaPF 6 and 1.2 V for aqueous electrolytes.…”

“…Based on first-principles molecular dynamics simulations, it has been calculated that the sizes of the first solvation shell of alkali ions in the EC solvent increase from Li + to Na + , that is, 1.95-2.34 Å (Cresce et al, 2017). The pore sizes of YP-50F are higher than 1 nm (Karamanova et al, 2019(Karamanova et al, , 2020, which means that they are accessible by solvated Li + and Na + ions. On the other hand, the bigger size of solvated Na + ions can be related with a worse rate capability of YP-50F in the NaPF 6 electrolyte.…”

“…All measurements were performed on Arbin Instrument System BT-2000 (United States). The specific capacitance was calculated from cyclic voltammograms and charge-discharge curves as described elsewhere (Karamanova et al, 2019(Karamanova et al, , 2020.…”

“…The advantages of biomass-derived carbons over others are the presence of diverse functional groups contributing to the extra charge storage in supercapacitors due to their participation in pseudocapacitance redox reactions (Bi et al, 2019). Recently, we have demonstrated that commercial coconut-derived carbons, possessing high amount of acidic groups and narrow pore size distribution, display excellent cycling stability in an alkaline electrolyte solution: the discharge capacitance decreases by only a 2% after 37,000 cycles (Karamanova et al, 2019(Karamanova et al, , 2020.…”

“…As biomass-derived carbons, commercial product YP-50F ("Kuraray Europe" GmbH) obtained from coconuts is employed. These products, possessing a high amount of acidic functional groups and narrow pore size distribution, are subjects of the study since they show magnificent cycling stability in aqueous LiOH and NaOH electrolytes (Karamanova et al, 2020). The interaction between the biomass-derived carbon electrodes and the organic electrolyte is examined on the basis of postmortem scanning electron microscopy (SEM)/energy-dispersive x-ray spectroscopy (EDS) and x-ray photoelectron spectroscopy (XPS) analyses of the electrodes after cell cycling.…”