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

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.

Promising Trade‐Offs Between Energy Storage and Load Bearing in Carbon Nanofibers as Structural Energy Storage Devices

“…Different types of energy storage devices such as batteries and supercapacitors4d,5 have been investigated for structural energy storage. Among them, supercapacitors show great potential as structural energy storage due to their rather simple laminated structure, which is similar to laminated structural composites 2b,6. Supercapacitors usually have a laminated structure which consists of two electrodes and a separator which is filled with electrolyte.…”

“…For instance, CFs activated with KOH with single fiber strength up to 3960 MPa were used in structural supercapacitors, but a relatively low SSA of 21.3 m 2 g −1 (compared to over 2000 m 2 g −1 for graphene) and a low capacitance of 2.63 F g −1 were achieved 14c. Various methods have been attempted to improve the capacitance of CF‐based supercapacitors by modifying CFs with nanomaterial such as CNT,6,14a conductive nanowire, and carbon aerogels . However, the capacitance of such capacitors is still relatively low compared to the graphene and CNT‐based counterparts 2a…”

Understanding the Mechanical and Conductive Properties of Carbon Nanotube Fibers for Smart Electronics

“…To realize the device application, the fiber structure is the first important issue to be considered as it determines the way to transfer/conduct load, current, and heat along the fiber and the way to interact with the surrounding medium and guest particles inside the fiber. For example, the assembly feature of CNT fibers and the high CNT alignment provide long charge transport paths which are very important for energy harvesting and storage in 1D devices, and the weaveability makes it possible to develop multifunctional fabrics …”

Multifunctional energy storage composite structures with embedded lithium-ion batteries

“…The multifunctional structural battery concept became an area of research interest almost two decades ago, with limited initial success [19][20][21][22]. However, researchers have since had further opportunities for advanced development of structurally integrated batteries (and capacitors and supercapacitors) following recent developments in tangentially-related technology fields, including material synthesis, characterization techniques, and computational modeling [22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40]. The first group of efforts represented a holistic, top-down approach that aimed for shape, packaging, and load path optimization of off-the-shelf batteries.…”

“…This approach is exemplified by numerous research efforts that include the introduction of structurallyenhanced polymeric or ceramic electrolytes [38][39][40][45][46][47], fiber-or particle-reinforced electrolytes and binder materials for the electrodes [23,48,49], novel structural materials with intercalation properties [24,27,34,50,51], and synthesis of energy storage materials in strong fibrous forms [36,52]. While many impressive results have been achieved in both cases, the intrinsic structural capabilities of the existing internal cell components are harnessed only marginally.…”