A 1.9-V all-organic battery-supercapacitor hybrid device with high rate capability and wide temperature tolerance in a metal-free water-in-salt electrolyte

HH Tsai and TJ Lin and B Vedhanarayanan and CC Tsai and TY Chen and XB Ji and TW Lin, JOURNAL OF COLLOID AND INTERFACE SCIENCE, 612, 76-87 (2022).

DOI: 10.1016/j.jcis.2021.12.124

Developing battery-supercapacitor hybrid devices (BSHs) is viewed as an efficient route to shorten the gap between supercapacitors and batteries. In this study, a composite hydrogel consisting of perylene tetracarboxylic diimide (PTCDI) and reduced graphene oxide (rGO) is tested as the anode for BSHs in the electrolyte of ammonium acetate (NH4Ac) with a record concentration of 32 molality (m). This water-in- salt electrolyte exhibits a wide electrochemical stability window of 2.13 V and high conductivity of 23.3 mS cm(-1) even at -12 degrees C. Molecular dynamics calculations and spectroscopic measurements reveal that a favorable water-acetate interaction occurs in a high concentration NH4Ac electrolyte. On the other hand, the study of electrode kinetics in 32 m NH4Ac demonstrates a high capacitive contribution to charge storage in PTCDI-rGO although an electrode redox reaction involves reversible enolization of carbonyl groups in PTCDI. This result suggests fast NH4+-ion intercalation kinetics in charge- discharge processes. Furthermore, the electrode performance is improved by optimizing the loading amount of rGO in composites. The best- performing composite electrode delivers the maximum capacity of 165 mAh g(-1) at 0.5 A g(-1) and sustains a great capacity retention of 66% at 8 A g(-1). Finally, an all-organic BSH device is tested in a broad temperature window from -20 to 50 degrees C and is well operated at 1.9 V regardless of operating temperatures. Due to the synergetic effect of splendid electrolyte properties and high anode capacities, BSH devices possess the maximum energy density of 12.9 Wh kg(-1) at the power density of 827 W kg(-1) and retain 74 % of the initial capacity after 3000 cycles at 1 A g(-1). Our study paves a novel route towards designing inexpensive and environmentally friendly BSH devices with high performances. (C) 2021 Elsevier Inc. All rights reserved.

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