Energy storage in multifunctional composites: Structural Energy Storage

Energy storage in multifunctional composites: Structural Energy Storage

Application of carbon fiber reinforced composite (CFRC) as light structural material in transport industry has been growing during the last 20 years because their unique combination of high specific stiffness and strength as well as toughness. Although aerospace applications is the main receptor of these materials, new commercial aircraft structures are made with more than 50 % in volume of CFRC, other transport systems (automotive, train, etc.) are also introducing CFRC in their vehicle structures. For example, necessity of lighter structures for electric cars has conducted to increase the composite components in them.
This research proposal is related with the development of multifunctional composites which, maintaining their structural properties, acquire the capability of energy storage. For it, the structural composite could be transformed into a supercapacitator. Structural laminate composites have a similar architecture as supercapacitors; for example: carbon fiber layers can behave as conductive parallel plates parallel separated by a thin resin film, which could act as a membrane allowing diffusion of ions but not flow of electrons. For it, two main objectives will be considered:

1) To increase the specific surface areas (SSA) of carbon fibers (CF) to behave as electrodes without loss of mechanical properties. For it, strategies (sizing and direct growth) based on addition of carbon nanotubes and/or graphene on the carbon fiber surface will be tested. Surface, mechanical and electrochemical characterization of modified carbon fiber will be carried out.
2) To develop a polymeric matrix that allows ionic diffusion but keeping the necessary stiffness for its application in CFRC structures. One strategy to be tested will consist in preparing blends of ionic liquids and structural epoxies that segregate and form two interpenetrating networks.

Our research group has previous experience on developing multifunctional composite by means the incorporation of carbon nanostructures (carbon nanotubes and graphene) into the CFRC. Composites with high electric conductivity for structural health monitoring, light-strike protection or anti-icing/de-icing applications have been developed. This route will be also explored in this proposal considering the direct growing or deposition of CNT and/or graphene on CF for increasing SSA with minimum degradation of mechanical properties. On the other hand, the application of solid polymer electrolytes (SPE) as matrix for structural composites could be also studied, although it could be necessary to increase their stiffness for structural applications. Beside, most polymers exhibit fluctuations in ionic transport when are subjected to environmental conditions, such as humidity. Studies on the capability of SPE to maintain operational integrity underwater or in wet/humid conditions will be also carried out.
The final objective of this proposal will be contribute to develop the technologies necessary for the future electric aircraft and automobiles; them it contributes to the thematic area “Energy efficiency & renewable energy: Smart transportation & mobility” although it is also related with “Smart energy systems: Energy storage”.