Quasi-solid-state supercapacitors based on wide-temperature eutectogels

Carbon-based supercapacitors possess fast charge-discharge rate, superior power density, and excellent cyclic lifespan, but it is subject to some problems, such as low operating potential window and energy density. To address these issues, a ternary deep eutectic solvent with a freezing point below −85.6 °C was firstly prepared using lithium perchlorate trihydrate and urea and then used as a reaction solvent to take part in a free radical polymerization reaction to prepare eutectogels. The optimized eutectogel showed an ionic conductivity of 20 mS cm−1 at room temperature and could be still stretched and twisted even at −40 °C. The quasi-solid-state supercapacitor composed of a eutectogel and carbon electrodes demonstrated a stable voltage window of 0–2.0 V, an energy density of 10.76 Wh kg−1 at a power density of 465 W kg−1 and excellent cycling stability with ∼105 % capacitance retention after 10,000 cycles. The flexible quasi-solid-state supercapacitors with such a eutectogel not only could be operated from −40 to 60 °C, but also exhibited a moderate bendability. Moreover, the damaged flexible quasi-solid-state supercapacitor could be still charged and drive a mini-fan for ⁓60 s. Therefore, the eutectogels displayed a promising potential for enhancing the energy density of carbon-based supercapacitors and should also provide instructive guidance for the preparation of wide-temperature gel polymer electrolytes.