A state of art review of structural batteries and their aeronautic potential was published. Requirements for aeronautic SB were assessed with active support of the industrial AB (Piaggio Aerospace, Pipistrel Vertical Solutions, FACC, Dassault Aviation), analysing electrochemical/mechanical/structural perspectives, manufacturing constraints and airworthiness and safety aspects.
A thermoplastic polymer-ionic liquid structural electrolyte and energy-dense composite electrodes were developed and implemented in 2 SB cell concepts: UNIVIE’s Coated Carbon Fibers (CCF), showing suitable mechanical performance but lower maturity in electrical performance and reproducibility, and AIT’s Reinforced Multilayer Stack (RMS), achieving around 50 Wh/kg and a Young’s modulus of 10 GPa. Their scalable manufacturing was demonstrated by AIT delivering 40 RMS SB cells for the SOLIFLY demonstrator.
An SB integration concept was developed by ONERA with a numerical strategy for integrating thin SB cells in solid CF composite laminates, quantifying the impact of the battery insert on the mechanical performance with respect to its size, shape and position in the structure. For the first time, the damage and failure process of the SB laminate was studied, and recommendations were established. The mechanical behaviour and failure properties of the two battery cell concepts were characterized by ONERA with multi-instrumented measurements for the use in numerical design such multifunctional structures. A modified curing cycle was developed that preserves the SB electrical properties and composite mechanical properties.
For final demonstration, the SOLIFLY multifunctional demonstrator, a stiffened CF composite panel integrating 20 AIT RMS SB cells in its skin, increasing weight only by 2.6%, and a monofunctional reference were designed by simulation for sustaining high uniaxial compression loading while fitting to ONERA’s test facility and manufactured. The global stiffness of both panels was found very similar, what validates the proposed design, while the first buckling load was reduced due to initial delamination introduced the electrical insulation of the SB cells. Still, the multifunctional panel was able to carry more than 18 tons without failure which matches our initial goal of the SOLIFLY project to produce a high-strength multifunctional part. 80% of the SB cells were electrically functional after curing and none of the controlled cells failed due to the mechanical test. To our knowledge, the SOLIFLY demonstrator is the first multifunctional stiffened panel with high mechanical properties that has been successfully manufactured and tested.
SOLIFLY has assessed the manufacturability of the developed multifunctional technology (CustomCells), identified TRL step up and examined certification aspects including first discussions with EASA specialists (UNINA). The potential of SB integration was studied at aircraft level showing that a considerable amount of electrical energy could be stored and even could contribute to hybrid electric propulsion (CIRA). A workshop and public event presented the project outcomes to the AB and a wider public, discussing in detail how structural batteries could contribute to future climate neutral air transport.
