F. Bozorgmehrian, M. Jeong, P.W. Vesely, J. Burger, R.J. Schick, O. Sasso, D. Jarrahbashi, H. Castaneda, A. Asadi
Texas A&M University,
United States
Keywords: structural battery composites, supercritical spray deposition, patterned surfaces
Summary:
The growing demand for zero-emission vehicles for urban, air and space mobility has reignited interest in battery-powered electric mobility (e-mobility). Particularly, reshaping aviation toward a greener future by 20501 will not be realized without addressing challenges in battery technology in electric flights and electric vertical take-off and landing (e-VTOL) aircrafts. Carbon fiber reinforced polymer battery composites (CFRP-SBCs), comprising polymers as electrolyte matrix and carbon fibers (CFs) as electrodes, collectors and reinforcements show a perfect synergy between structural performance and energy efficiency. However, a significant hurdle is the considerably lower energy density (less than 40 Wh/kg in full cell configuration)2-4 compared to the conventional batteries as well as the minimum required 400-600 Wh/kg for small-medium size planes5, and their significantly reduced strength and stiffness (2-10 GPa modulus and ~100-200 MPa strength, 20-30% of structural CFRPs). This is arising from the inherent tradeoff between mechanical and electrochemical properties and the historical separation of batteries and structures. This is a common trait in almost all engineered materials, in which efforts to enhance multiple functions, such as energy storage and structural properties, face complexity as improvements in one compromise others. Particularly in CFRP-SBCs, two bottlenecks to achieve simultaneous high energy density and high mechanical strength are: (1) Very low ion transport in solid polymer electrolytes (10-6-10-5 S.cm-1) compared to liquid (10-2 S.cm-1) and ceramics (10-5-10-3 S.cm-1). (2) Requirement of abundant coating of active materials on carbon fiber cathodes to reach reasonable energy density that results in weakening the interfacial adhesion with the electrolyte (and separator) that causes delamination and premature mechanical failure. Herein, we introduce a scalable and green manufacturing technique without the use of harsh solvents, wherein engineered patterns are fabricated on cathode to create tailorable microstructure for simultaneously high strength and high energy density in CFRP-SBCs. We introduce a novel, scalable and sustainable processing-manufacturing technology, in which a combination of supercritical CO2 spray technique and tailorable materials chemistry (via engineering amphiphilicity) allows creation of 3D patterns on carbon fiber based cathodes. These patterns are combined to create desired 3D nanostructures to achieve tailorable properties. To this end, the droplet size and amphiphilicity degree of the hybrid material system contained in droplets, i.e. lithium iron phosphate (LFP) and reduced graphene oxide (RGO), are engineered based on their mass ratio and then delivered onto the carbon fibers using the supercritical CO2 spray. The droplet sizes are in the range of 5 µm, as the small microscale droplets allow for faster fabrication of cathode with higher surface area that incurs higher interface with the developed electrolyte. The combination of amphiphilicity and droplet size results in three distinctive post-evaporation patterns, i.e. ring, disk, and dome. Each pattern is meticulously designed to enhance a specific functionality or property. By strategically composing these patterns with precise shape, size, and spacing, we achieve the creation of 3D nanostructured surfaces that exhibit both high energy density and exceptional mechanical strength, qualities often deemed paradoxical and unattainable with conventional manufacturing methods.