Temperature-dependent performance of carbon-based supercapacitors with water-in-salt electrolyte

Water-in-salt (WIS) electrolytes are successfully introduced into carbon-based supercapacitors to effectively promote energy density. However, temperature-dependent performance of carbon-based supercapacitors with these electrolytes is rarely discussed, and the key factors, determined electrochemical performance at a wide temperature range, are not revealed completely. Herein, three rose petal-derived porous carbons (RPC) with different pore properties are prepared by a KOH activation strategy. The electrochemical performance of RPC-based supercapacitors with different concentration LiTFSI WIS electrolytes is investigated from −20 to 100 °C. The working voltage of these supercapacitors can reach 2.4 V, and thus the energy density of RPC supercapacitors with 20 m LiTFSI electrolyte can highly attain 44 W h kg−1 at 564 W kg−1 and 60 °C. Even though the power density is 3.5 kW kg−1 at 25 °C, it can be maintained to 12 W h kg−1. More importantly, the electrochemical performance intimately depends on the temperature. Both electrolyte concentration and pore properties of RPC significantly influence the electrochemical performance of these supercapacitors at different temperature. Therefore, to achieve superior performance for carbon-based supercapacitors with the LiTFSI WIS electrolyte at a wide temperature range, the optimization of electrolyte concentration and rational design for pore properties of carbon materials are essential strategies.