This Small Business Innovation Research (SBIR) Phase II project addresses the development of a multifunctional solid-state nanolaminate composite, which may function as a structural material while storing energy in the form of a rechargeable super-capacitor. A unique production process is used, where liquid monomer and aluminum wire are introduced into a process chamber that converts them into a multilayer composite with thousands of polymer and aluminum layers. Applications include storage devices for battery back-up and inverter circuits used in transportation and high energy density capacitors for extreme thermo-mechanical environments, such as aircraft, photovoltaics and aerospace. The Phase I development work demonstrated the production of large area (10sq.ft.) energy storage material. The nanolaminate material has mechanical properties that are close to a hard polymer laminate and energy densities which are an order of magnitude higher than conventional electrostatic capacitors and similar to those of electrochemical super-capacitors, with superior performance at temperatures below -20C and above +65C. The Phase II effort includes development work to optimize certain manufacturing methods, optimization of the polymer dielectric, packaging development, creation of specification sheets based on short and long term life tests and sampling potential customers that represent immediate and long term business opportunities.
The broader impact/commercial potential of this project is in the utilization of a new multifunctional material that can store energy. Such material may be integrated into a structure and save space and weight. It is a green product that requires no water or solvents to produce, it is recyclable and it does not involve the use or disposal of hazardous materials. Nanolaminate energy storage products will be based on mainly two materials, aluminum wire and acrylate monomers, which are commonly used to produce protective coatings for flooring, printing, furniture, window films, etc. Lightweight energy storage nanolaminates can replace double layer electrochemical super-capacitors that have severe temperature limitations and conventional electrostatic capacitors, in applications where volume, weight and thermomechanical constraints such as vibration and operating temperature are limiting factors. Capacitors produced using nanolaminate composites, are solid-state components that can electrically self-heal and have an open-circuit, or fuse-like safe failure mode, which is desirable in applications such as electric vehicles and aircraft, where safety of people in the proximity of a capacitor bank is of paramount importance. Multifunctional materials are expected to play a key role in the future in improving energy efficiencies and reducing dependency on fossil fuels.
The project objective was the development of Polymer Multi Layer (PML) capacitors in the form of large area laminates that utilize submicron electron beam cured polymer dielectrics and metallized electrodes. Such energy storage capacitors can be integrated into electric vehicle structural panels, doors, roof, and trunk, to reduce volume and weight. Large area nanolaminates with a thickness of 2-3mm, an area of 10sq.ft and up to 6,000 polymer dielectric and electrode layers, were produced and evaluated for electrical and structural properties. The project demonstrated that PML capacitor laminates formed with submicron amorphous polymer dielectrics have superior breakdown strength (>1000V/mm) when compared to that of conventional polymer films. While addressing near term market opportunities for such capacitor technology, DC-Link capacitors that are used in the inverter circuit of hybrid and electric vehicles were identified as a potential opportunity. The DC-Link capacitor is one of the largest, costliest, and most failure-prone components in today’s electric drive inverter systems. Current DC-Link capacitors utilize wound metalized polypropylene film capacitors that have low energy density and poor reliability at higher temperatures. PML capacitors designed for DC-Link applications segmented from a large area 4,000 layer laminate, were shown to have stable dielectric constant in the temperature range of -40oC to 160oC, dissipation factor <0.01, excellent self-healing properties, low ESR and ESL, and energy density >3X that of conventional metallized PP capacitors. Pursuing alternative applications with lower entry barriers, such as pulse power and defibrillators, 2,000 layer PML capacitors with 0.65mm thick polymer dielectric, operated at 500VDC were produced with an active volume energy density of 8J/cc. This is a record energy density for an electrostatic capacitor with stable polymer dielectric properties. At this voltage level, the capacitor dielectric is stressed at 770V/mm, which is higher than the intrinsic breakdown strength of conventional polymer dielectric films. This record breakdown strength performance is due to the development of amorphous, pinhole free polymer dielectric materials combined with the finding that as the thickness of a polymer dielectric decreases the breakdown strength increases. Thus capacitors produced with sub-micron dielectrics have superior energy density. In summary, this NSF project succeeded in demonstrating that it is possible to produce large area laminates comprising thousands of nanothick polymer dielectric layers and nanothick metallized electrodes, with significant structural strength and flexibility, to allow integration into structural panels of vehicles to reduce weight and volume. Although implementation and industry acceptance of such energy storage structural laminates will take some years to develop, the project also demonstrated that such large area laminates can function as a "mother" capacitor material from which smaller capacitors can be segmented and processed into unique products, for applications that demand a combination of high temperature performance and high energy density.
