Beyond structural; multifunctional composites that store electrical energy

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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.