Beyond structural; multifunctional composites that store electrical energy

Smart structures, in which monofunctional devices (e.g. sensors, actuators or batteries) and structural materials are sandwiched together, can provide elegant technical solutions to engineering problems. However, they offer limited space and weight savings: ultimately their efficiency is controlled by the interfaces between the device and the surrounding structure. A radically different concept is one in which the constituents (i.e. fibres and matrices) of the structural material themselves are multifunctional, acting in synergy to give truly multifunctional materials which inherently perform two (or more) functions simultaneously. This proposal focuses on structural supercapacitors, in which the material provides two disparate functions: mechanical load bearing and electrical energy storage. Such devices offer important performance advantages in minimising system weight and volume, and present opportunities for innovative design. It is notable that there are several synergies between energy storage devices and polymer composites: the laminated architecture of such materials mirrors the electrode configuration in supercapacitors. Furthermore, both devices use carbon based reinforcements/electrodes infused with a polymeric matrix/electrolyte. Such parallels provide a strong motivation for wedding these two disparate fields to develop structural power materials.

Supercapacitors consist of two high surface area electrodes, an electrolyte and a separator: charge is collected reversibly at the electrolyte/electrode interfaces. Their performance makes them useful as high power sources and, when used in conjunction with batteries, life extension for power sources for electric vehicles. For structural supercapacitors, there are two multifunctional components: a structural reinforcement/electrode, and a structural separator/electrolyte. Through our research in this field we have identified three critical challenges for structural supercapacitors: we will address these in this proposal. We will significantly improve how much electrical energy these devices can store (i.e. energy density), how quickly they can be charged or discharged (i.e. power density) and their mechanical performance. To improve energy density, we will develop reinforcements/electrodes with increased surface areas and electrochemical activity. In parallel, we will formulate matrices/electrolytes which are stiff and robust, thus giving enhanced mechanical performance, but with greater ionic conductivity, and hence power densities. In bringing the best constituents together to form multifunctional composites, we will exploit both existing architectures, developed in our previous work, and develop new ones. The project will culminate in demonstration of the best devices through fabrication and testing of industry inspired components.

Once mature, this class of multifunctional structural energy storage materials will have a huge impact on applications such as aerospace, automotive and portable electronics. For instance, imagine future tablet computers with no batteries, in which the electrical energy is stored in the casing material. Consider electric cars, in which the bonnet, doors and roof store all the energy to power the vehicle. Meeting such ambitions will have a profound effect on future engineering structures and will inspire others to work in this exciting field.

The breadth of potential applications and the simplicity of the concept of structural power has drawn considerable interest from academia, industry and the public to our work. However, it is apparent that there is a need for practical demonstrators with defined performance parameters before industry can consider adopting this technology for their own products. Although structural power straddles two critical technologies (polymer composites and energy storage), the developments to date have been driven by the Composites Sector, which is currently undergoing phenomenal growth, compelled by widespread adoption in sectors such as Automotive. However, additional opportunities for this novel technology have emerged, such as the aspiration of Airbus to have a fully electric powered passenger aircraft by 2050: this ambition will be underpinned by both lightweighting and energy storage solutions. Structural power goes well beyond Transportation: for example, we foresee that these materials will be exploited in areas such as mobile electronics and portable tools.

To maximise the impact, we have drawn together material suppliers, research institutes and end-users who will form the industrial advisory board (IAB). Throughout the project they will attend six-monthly meetings to monitor and guide the direction of the research. Most importantly, towards the culmination of the project they will inspire our demonstrator selection by identifying applications for early adoption of this technology. To further dissemination we will publish in the highest quality in high impact journals, which will solidify UK's leading position in structural power materials. This dissemination will be further supported by presentation at international composite, materials (chemistry) and electrochemistry conferences, participation at which also provides excellent networking opportunities. Events such JEC will provide focused industrial exposure.

We have strong links with the leading Groups in structural power, such as in the US, Sweden and Korea. In addition, we will exploit the burgeoning interest in structural power to provide opportunities to collaborate with the sixty or so companies who have approached us about this technology. Organisations such as the Energy Futures Lab at Imperial College and Durham Energy Institute will have opportunities to promote the research, facilitate collaborations and exploit the technology. The IAB will also provide a mechanism for initiating collaboration and development of these materials beyond the life of the project. Regarding outreach to the general public, our track record is excellent, with the PI having received huge attention with newspaper articles worldwide. This mechanism proved to be one of the most effective to attract potential industrial collaborators. We will build on this experience to produce a website, including highly effective press releases accompanied by video-clips on Youtube, and present at events such as Imperial Festival. At the culmination of the project we will develop the model of a previous successful industrial engagement day held at NCC on ductile composites. Finally, we will train four highly skilled researchers in multifunctional material synthesis, characterisation and utilisation, with their work having been directly exposed to industry via the IAB. These interdisciplinary experts will be potential champions for technology transfer activities or other developments of the technology.

In summary, this proposal on structural power is a timely opportunity to make a significant impact in delivering new technologies and training engineers to address such future societal challenges associated with energy storage and lightweighting.