Energy storage in structural composites by introducing CNT fiber/polymer electrolyte interleaves

TL;DR

This paper introduces a novel method to create structural composites that can store energy, combining electrical and mechanical functions by integrating CNT fiber/polymer electrolyte interleaves within carbon fiber composites, achieving high energy and power densities.

Contribution

The work demonstrates a new approach to produce structural supercapacitors with integrated energy storage and mechanical strength, including innovative interleaves and hierarchical structures.

Findings

Achieved high specific capacitance of 88 mF/g.

Reported maximum power density of 30 W/kg.

Maintained electrochemical performance up to fracture.

Abstract

This work presents a method to produce structural composites capable of energy storage. They are produced by integrating thin sandwich structures of CNT fiber veils and an ionic liquid-based polymer electrolyte between carbon fiber plies, followed by infusion and curing of an epoxy resin. The resulting structure behaves simultaneously as an electric double-layer capacitor and a structural composite, with flexural modulus of 60 GPa and flexural strength of 153 MPa, combined with 88 mF/g of specific capacitance and the highest power (30 W/kg) and energy (37.5 mWh/kg) densities reported so far for structural supercapacitors. In-situ electrochemical measurements during 4-point bending show that electrochemical performance is retained up to fracture, with minor changes in equivalent series resistance for interleaves under compressive stress. En route to improving interlaminar properties we produce grid-shaped interleaves that enable mechanical interconnection of plies by the stiff epoxy. Synchrotron 3D X-ray tomography analysis of the resulting hierarchical structure confirms the formation of interlaminar epoxy joints. The manuscript discusses encapsulation role of epoxy, demonstrated by charge-discharge measurements of composites immersed in water, a deleterious agent for ionic liquids. Finally, we show different architectures free of current collector and electrical insulators, in which both CNT fiber and CF act as active electrodes.