Organic ionic conductors infused aqueous inverse-melting electrolyte aiding crack recovery in flexible supercapacitors functional down to −30 °C

Abstract

The advent of foldable mobiles and electronic devices has persuaded the need for the development of safe, robust and durable flexible energy storage devices. With global temperatures plunging well below 0 °C in most parts of the globe during winters, it is vital to enhance the low temperature performance of these energy storage devices. Aqueous electrolytes for supercapacitors and batteries offer the most sustainable solution when compared to electrolytes made of organic solvents or ionic liquids. Here, we report an inverse-melting pluronic polymer gel electrolyte (PPGE) consisting of an amphiphilic pluronic polymer/water mixture that acts as a cryoprotectant thereby rendering flexible supercapacitors operational down to −30 °C. Organic ionic conductors (OIC) were introduced into the PPGE to boost ionic conductivity. The fabricated supercapacitors exhibit a specific capacitance of 436 Fg-1 and 441 Fg-1 at 25 °C with PiHI and PiBr as OIC, respectively (at 1 Ag-1 current density). The same devices have a significantly higher capacitance of 140 Fg-1 and 339 Fg-1 at −30 °C. A maximum energy density of 16.8 Wh/kg and 11.77 Wh/kg were obtained at 25 °C and −30 °C, respectively. Additionally, the device with PiBr exhibits high capacitance retention of 70% at −30 °C. Furthrmore, the fabricated devices exhibit cooling performance recovery.