In this work, we report the synthesis of a high ionic conducting and mechanically stable non-aqueous gel polymer electrolyte (GPE) in which a liquid electrolyte (LiClO₄/propylene carbonate) is entrapped in a poly(2-hydroxy-3-phenoxy propyl acrylate) matrix by a UV assisted in situ polymerisation strategy. Unlike conventional dry and quasi-solid non-aqueous GPEs, our system (H-P-L-3M-80%) shows an excellent ionic conductivity of 4.7 × 10⁻³ S cm⁻¹, a value which is comparable to those of non-aqueous liquid electrolytes. The high mechanical stability of GPE arises due to the covalent cross-links present in the polymer matrix as well as the reversible non-covalent cross-links between the solvent and the polymer matrix through the Li⁺ cations. Subsequently, the GPE has been prepared in situ on the inner and the outer surface of the electrode material to fabricate a 2.0 V supercapacitor device with a high mass loading (3.8 mg cm⁻²) of the active material (YP-80F, a high surface area porous carbon). The device shows an equivalent series resistance (ESR) as low as 2.2 Ω, which is close to that of the device fabricated from the corresponding liquid electrolyte and is far better than those of the devices evolved from conventional GPEs and dry polymer electrolytes. The mass specific capacitance of 113 F g⁻¹ obtained at a current density of 2 mA cm⁻² shows 81% retention even at a high current density of 20 mA cm⁻². The scalability of the strategy is demonstrated by fabricating a large area (area = 16 cm², loading = 4.0 mg cm⁻²) all-solid-state flexible-supercapacitor (H-P-L-3M-S-4.0) device which can be operated at a potential window of 2.5 V. The device was found to show a mass specific capacitance of 111 F g⁻¹ at a current density of 1 mA cm⁻² (0.25 A g⁻¹), all the while, retaining a very low ESR of 2.2 Ω. The potential of the strategy to mimic the liquid-like electrode–electrolyte interface, augmented with the ability to tune further, opens up new horizons for energy storage devices.

We report the design of an all-solid-state supercapacitor, which has charge storage characteristics closely matching that of its liquid-state counterpart even under extreme temperature and humidity conditions. The prototype is made by electro-depositing polyethylenedioxythiophene (PEDOT) onto the individual carbon fibers of a porous carbon substrate followed by intercalating the matrix with polyvinyl alcohol–sulphuric acid (PVA–H₂SO₄) gel electrolyte. The electrodeposited layer of PEDOT maintained a flower-like growth pattern along the threads of each carbon fiber. This morphology and the alignment of PEDOT led to an enhanced surface area and electrical conductivity, and the pores in the system enabled effective intercalation of the polymer–gel electrolyte. Thus, the established electrode–electrolyte interface nearly mimics that of its counterpart based on the liquid electrolyte. Consequently, the solid device attained very low internal resistance (1.1 Ω cm⁻²) and a high specific capacitance (181 F g⁻¹) for PEDOT at a discharge current density of 0.5 A g⁻¹. Even with a high areal capacitance of 836 mF cm⁻² and volumetric capacitance of 28 F cm⁻³, the solid device retained a mass-specific capacitance of 111 F g⁻¹ for PEDOT. This is in close agreement with the value displayed by the corresponding liquid-state system (112 F g⁻¹), which was fabricated by replacing the gel electrolyte with 0.5 M H₂SO₄. The device also showed excellent charge–discharge stability for 12 000 cycles at 5 A g⁻¹. The performance of the device was consistent even under wide-ranging humidity (30–80%) and temperature (−10 to 80 °C) conditions. Finally, a device fabricated by increasing the electrode area four times was used to light an LED, which validated the scalability of the process.