Performance Characterization of Multifunctional Structure-Battery Composites for Marine Applications

Abstract

The aim of our work is to design, fabricate and characterize multifunctional structure-power composites for marine applications such as in unmanned underwater vehicles. Three types of structure-power (or structure-battery (SB)) specimens were fabricated using fiber-reinforced polymers and closed-cell foam as the structural components, and commercial-off-the-shelf lithium-polymer cells as the power-plus-structure component. This paper details the mechanical and electrical characterization of the S-B composites while a companion paper deals with the design and fabrication issues. The three multifunctional designs are: integrated SB laminate with lithium-polymer pouch cells embedded on one side, SB sandwich with cells embedded within a closed-cell polymeric foam along the neutral axis, and a SB modular stiffener that can be attached and removed from a host-structure. Unifunctional composites (i.e. without embedded cells) were also fabricated for comparison with the multifunctional composites. The embedded cells show identical charge-discharge electrical performance as their un-embedded counterparts, thus, indicating that the composite fabrication procedures did not adversely affect their electrical performance. Ragone curves (energy density vs. power density) of the S-B composites show that the targeted energy density of 50 Wh/L was achieved in the SB modular stiffener design. The bending stiffnesses of the integrated SB and SB modular stiffener designs were ∼7x greater than the unifunctional design while the multifunctional sandwich specimens were ∼17% stiffer than their unifunctional counterparts. Tests are currently being conducted to determine the affect of mechanical flexure (constant displacement) on embedded cell discharge and charge characteristics, and conversely, cell discharge and charge on the load and deflection during flexure.