High-rate performance aqueous-based supercapacitors at −30 °C driven by novel 1D Ni(OH)2 nanorods and a two-solute electrolyte.

Extreme application environments, such as the exploration of space and living in polar regions, require electrochemical energy storage devices to operate well at ultralow temperatures. Aqueous-based supercapacitors (ASCs) have attracted much attention because of their high safety, high-rate performance, and long cycle-life. However, their application in low-temperature environments is also severely limited by the high freezing point of the aqueous-based electrolyte. In this paper, based on the ability of the coordination between Ni²⁺ and Cl⁻ to restrict the longitudinal growth of Ni(OH)₂ along the (0 0 1) crystal plane and the inherent ultralow freezing point of NaCl aqueous solution, cost efficient NaCl was explored for its ability to both regulate the preparation of one-dimensional (1D) Ni(OH)₂ nanorods and develop a two-solute electrolyte for ASCs with ultralow-temperature resistance. The 1D Ni(OH)₂ nanorods comprised bundles of finer nanorods with a diameter of about 16 nm, which could authentically shorten the transport distance of OH⁻ and electrons, providing enough deformation space for them to interact with each other. Both the three-electrode system and assembled ASCs using this electrode material of 1D Ni(OH)₂ nanorods were used to test the specific capacitances, and it was found that this material could give 1.6 times higher values than those of 2D Ni(OH)₂ nanosheets at the corresponding scan rates or current densities. Further, the capacitance retention was found to gradually increase from 84.04% for NO0//AC to 96.24% for NO16//AC after 10 000 cycles at 5 A g⁻¹. With the assistance of the two-solute electrolyte, the capacitance retention of NO16//AC at −30 °C was up to 61.1% from 0.5 to 10 A g⁻¹, and 90.21% after 10 000 cycles at 5 A g⁻¹. These results demonstrate not only the potential application of low-cost NaCl in energy storage systems, but also the application of ASCs in ultralow-temperature environments. [ABSTRACT FROM AUTHOR]