The redefinition of commonly named “water-in-salt” clarifies the operating temperatures of the state-of-the-art LiTFSI-based aqueous solutions. An in-depth study shows its mismatch for low temperature applications. Contrariwise, the recommended strategy...

Safer-by-design and sustainable energy storage devices are envisioned to be among the required 2.0 solutions to satisfy the fast growing energy demands. Responding to this evolution cannot be freed from a global and synergetic approach to design the requisite electrolytes taking into account the toxicity, the eco-compatibility and the cost of their constituents. To target low-temperature applications, a non-toxic and costefficient eutectic system comprising LiNO 3 in water with 1,3propylene glycol as co-solvent was selected to design a ternary electrolyte with a wide liquid range. By using this electrolyte in an electrochemical double-layer capacitor (EDLC), the operating voltage of the device reaches an optimum of 2.0 V at À 40 °C over more than 100 h of floating. Moreover, after being set up at 20 °C, the temperature resilience of the capacitance is near total, demonstrating thus a promising feature related to the suitable thermal and electrochemical behaviours of the tested EDLC devices.

Conventional manganese oxide (MnO2)‐based supercapacitors struggle to achieve theoretical capacitance due to the material's low conductivity and large particle size. Consequently, researchers have improved MnO2's properties by incorporating conductive carbonaceous materials to obtain high‐performance composite materials. Herein, the full process of engineering a MnO2‐graphene oxide (GO) composite and its application as a positive electrode for asymmetric supercapacitors (ASC) is presented. First, GO using a novel gas expansion precursor allowing an efficient chemical exfoliation of pristine graphite is synthesized. Afterward, size‐weakened MnO2 nanoparticles are synthesized and deposited onto the GO sheets by a self‐assembly redox reaction method using different MnO2/GO mass ratios. Multiple characterization methods are used to investigate the textural and structural properties of each material. A general electrochemical characterization is conducted using a three‐electrode cell; therefore, the synthesized MnO2‐GO composite achieves 150 F g−1 at 10 mV s−1. Furthermore, an ASC in an aqueous electrolyte using GO and MnO2 or MnO2‐GO as negative and positive electrodes, respectively, is assembled. The fabricated ASC based on MnO2‐GO composite exhibits a high specific capacitance of 38 F g−1 at 1 A g−1, excellent cycling stability after 36 000 cycles, and a steady electrochemical impedance behavior after 120 h of floating.