Hybrid lithium-ion supercapacitors combine the advantages of both the high power density of capacitors and the high energy density of lithium batteries, where activated carbon serves as a critical cathode material with an electric double-layer capacitance charge storage mechanism. Here, we have demonstrated that a new activated carbon, which was prepared by the calcination of deoxygenated agar, can greatly enhance the specific energy of the hybrid lithium-ion supercapacitor, assembling with a multilayer "protected-lithium anode" and 21 m LITFSI "water-in-salt" electrolyte. The obtained carbon material has a suitable pore volume and narrow pore-size distribution and shows a high specific surface area up to 1672 m2 g-1 and a high specific capacitance of 210.4 F gAC -1 in "water-in-salt" electrolyte. The assembled hybrid lithium-ion supercapacitor shows a high specific energy of 308.3 W h kgAC -1 at a specific power of 0.7 kW kgAC -1. In addition, it presents an encouraging 89% retention of the initial specific energy after 8000 charge/discharge cycles. The improvement can be attributed to the high surface area of the carbon material and its narrow pore-size distribution, the wide operation potential window of "water-in-salt" electrolyte, and the high cell working voltage by using protected-lithium anode.
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