An energy and power dense aqueous zinc-ion hybrid supercapacitor with low leakage current and long cycle life

Imparting high energy density to already power dense capacitor leads to hybrid supercapacitor (SC), which is most sought after in automobile, heavy-duty electronics application, and internet of things. The hybrid SCs with lithium or sodium ion chemistry demand organic electrolytes for their operation, which is environmental unfriendly and poses fire-hazard. As an alternative, here we report a low cost and highly safe energetic hybrid SC based on zinc-ion chemistry operated in 3 M ZnSO4 with high surface area (1018 ± 4 m2 g−1) hierarchical porous carbon cathode material derived from the Tamarindusindica seeds (ACTS-800), a bio-source. The hybrid SC demonstrates a maximum energy density of 127 (± 3) Wh kg−1 (254 μWh cm−2) at 0.1 A g−1 and power density of 7920 (± 24) W kg−1 (15.84 mW cm−2) at 10 A g−1. Besides having excellent power/energy density values, ∼ 100% capacity retention over 5000 galvanostatic charge/discharge cycles was observed. The most interesting feature of this SC is its low open-circuit voltage decay (34% in 60 h) and low leakage current density (11 mA g−1), which allows it to hold charge for longer duration qualifying it as one of the best aqueous SC known in the literature.