Mechanical, electrochemical and multifunctional performance of a CFRP/carbon aerogel structural supercapacitor and its corresponding monofunctional equivalents

Abstract

This work investigated and developed a protocol for establishing the multifunctional performance of a structural supercapacitor: a composite which can simultaneously carry mechanical load whilst storing electrical energy. The Structural Supercapacitor consisted of carbon aerogel (CAG) reinforced carbon fibre (CF) electrodes which sandwiched a woven glass fibre lamina and was infused with a structural electrolyte (SE). This was compared to two monofunctional devices: a Monofunctional Supercapacitor and a Monofunctional Laminate in which the SE had been replaced by ionic liquid and a structural epoxy, respectively. In the Monofunctional Supercapacitor, the considerable surface area of the CAG and ionic capacity of the liquid electrolyte resulted in a high device normalised capacitance (1731 mF/g). However, in the Structural Supercapacitor the SE presented meso-scale heterogeneity, obstructing the CAG pores with thin films of epoxy. This resulted in a considerable reduction in electrochemical performance, with a drop in the device normalised capacitance to 212 mF/g. Regarding mechanical performance, it was shown that the CAG had promoted brittle fracture, leading to a severe depression in the tensile and in-plane shear strengths. The Structural Supercapacitor presented a tensile modulus and strength of 33 GPa and 110 MPa, respectively: a 15% and 11% drop in tensile modulus and strength, respectively, compared to that of the Monofunctional Laminate. However, under in-plane shear the soft SE dominated, leading to about a 44% drop in shear modulus (1.7 GPa) and strength (13.7 MPa at 1% shear strain). This work has provided an insight into the hurdles associated with demonstrating multifunctionality, including the scaling challenges for electrochemical and mechanical characterisation and the need to report both active material and device normalised data. The emergence and development of such structural power composites could address the issue of parasitic battery mass in transportation, and hence realise full electrification of aircraft and cars.

A critical review of structural supercapacitors and outlook on future research challenges

“…Whilst presenting data using structural electrolytes, some researchers have also shown data on the device using a liquid electrolyte. This approach provides useful comparisons of the electrochemical performance when changing from a monofunctional (i.e., liquid electrolyte) to a multifunctional device (i.e., structural electrolyte) [22].…”

“…Other reporting ambiguities are indicated in the Table legends. One clear outcome from this review is the need for a protocol to compare data from across the literature [22], and hence to identify the most promising routes to realising high performance structural supercapacitors.…”

“…2. Relative proportion (by mass) of constituents in single cells, excluding encapsulation, of (a) conventional supercapacitor [24]; (b) typical structural supercapacitor [22]. multiwall nanotubes.…”

Multifunctional design, feasibility and requirements for structural power composites in future electric air taxis

“…10 One approach has been to use carbon aerogel (CAG), the precursor for which is infused through the dry fabric and then pyrolyzed to yield a CAG monolith which supports the CFs. CAG provides a high specific surface area of 121 m 2 /g 11 (giving high capacitance), fills the matrix space and mechanically supports the fibres. 12 However, CAG is brittle which impacts on the durability and device processability.…”

“…17 SSCs have experimentally demonstrated the following multifunctional device properties: E = 33 GPa, σ = 110 MPa, Γ * = 1.4 Wh/kg and P * = 1.1 kW/kg. 11,18 The mechanical properties were obtained from longitudinal tensile coupon tests on unidirectional SBCs or plain weave SSCs. Multicell SSC demonstrators have been manufactured, including an automotive boot lid 7 (Figure 2(b)) and a fuselage rib that powers a desktop-scale aircraft door to open and close 16 (Figure 2(c)).…”