Multifunctional Carbon Fiber Composites: A Structural, Energy Harvesting, Strain-Sensing Material.

Multifunctional structural materials are capable of reducing system level mass and increasing efficiency in load-carrying structures. Materials that are capable of harvesting energy from the surrounding environment are advantageous for autonomous electrically powered systems. However, most energy harvesting materials are non-structural and add parasitic mass, reducing structural efficiency. Here, we show a structural energy harvesting composite material consisting of two carbon fiber (CF) layers embedded in a structural battery electrolyte (SBE) with a longitudinal modulus of 100 GPa─almost on par with commercial CF pre-pregs. Energy is harvested through mechanical deformations using the piezo-electrochemical transducer (PECT) effect in lithiated CFs. The PECT effect creates a voltage difference between the two CF layers, driving a current when deformed. A specific power output of 18 nW/g is achieved. The PECT effect in the lithiated CFs is observed in tension and compression and can be used for strain sensing, enabling structural health monitoring with low added mass. The same material has previously been shown capable of shape morphing. The two additional functionalities presented here result in a material capable of four functions, further demonstrating the diverse possibilities for CF/SBE composites in multifunctional applications in the future.

Shape-morphing carbon fiber composite using electrochemical actuation.

Structures that are capable of changing shape can increase efficiency in many applications, but are often heavy and maintenance intensive. To reduce the mass and mechanical complexity solid-state morphing materials are desirable but are typically nonstructural and problematic to control. Here we present an electrically controlled solid-state morphing composite material that is lightweight and has a stiffness higher than aluminum. It is capable of producing large deformations and holding them with no additional power, albeit at low rates. The material is manufactured from commercial carbon fibers and a structural battery electrolyte, and uses lithium-ion insertion to produce shape changes at low voltages. A proof-of-concept material in a cantilever setup is used to show morphing, and analytical modeling shows good correlation with experimental observations. The concept presented shows considerable promise and paves the way for stiff, solid-state morphing materials.