Tailoring molecular interaction in heteronetwork polymer electrolytes for stretchable, high-voltage fiber supercapacitors

Abstract

Mechanically and electrochemically stable all-solid-state supercapacitors are of great interest in the field of wearable and portable electronic devices. However, when conventional liquid or gel electrolytes are used in supercapacitors, their discontinuous functions appear in harsh external environments. Here, we prepare freeze-tolerant heteronetwork nanohybrid polymer electrolytes (NPEs), composed of hydrophilic poly(lithium acrylate) (PLiA) containing mobile lithium countercations and mechanically robust silica nanoparticles (SNs) serving as stress buffers, via sol–gel reaction and radical polymerization. The combination of PLiA and SN provides NPE (PLiA-SN) with high room temperature ionic conductivity (up to σDC ∼ 10-1 S/cm), which not only remains 100% even after 700% elongation, but also exhibits high ionic conductivity at low temperatures (σDC = 4×10-3 S/cm at 0 °C). This is because Li+ binds strongly to water, thereby preventing water evaporation and crystallization, as revealed by density functional theory (DFT) calculations. The cross-linking of SNs with PLiA chains also gives the resultant NPE superelasticity and self-healing property. The optimized NPE is assembled with metal–organic framework derived carbon (MDC)-coated carbon nanotube yarn (MDC@CNTY) hybrid electrodes, possessing both high charge storage capability and superior mechanical properties, to fabricate high-performance all-solid-state fiber supercapacitors (FSCs). The assembled FSC delivers a high specific capacitance of 51 F/g, high power (6 kW/kg, 27 mW/cm2, 1202 μW/cm) and energy (44 Wh/kg, 0.2 mWh/cm2, 9 μWh/cm) densities, as well as a wide operating voltage window as high as 2.5 V. Moreover, the electrochemical performance of the FSC is maintained under different stretching strains, various degrees of bending, and cutting/healing cycles, and still retains ∼ 92% capacity even at a low temperature (-10 °C), demonstrating excellent mechanical, thermal, and electrochemical stability. This work provides an effective strategy for designing energy storage devices that are sufficiently stretchable, bendable, and reliable for use in extreme environments.