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

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 (NHAc) 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 even at -12 °C. Molecular dynamics calculations and spectroscopic measurements reveal that a favorable water-acetate interaction occurs in a high concentration NHAc electrolyte. On the other hand, the study of electrode kinetics in 32 m NHAc 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 NH-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 at 0.5 A g and sustains a great capacity retention of 66% at 8 A g. Finally, an all-organic BSH device is tested in a broad temperature window from -20 to 50 °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 at the power density of 827 W kg and retain 74 % of the initial capacity after 3000 cycles at 1 A g. Our study paves a novel route towards designing inexpensive and environmentally friendly BSH devices with high performances.